Well, you have theory and you have whether or not it actually works. You could do this same mental exercise with a full-sized machine, too, but it would just make you nuts. In either machine, what you'll have is a whole lot of really hot water and detergent splashing around all over the place in there. That's pretty much it. All machines operate exactly the same this way. All have "theoretical" dead spots but there's so much water splashing around for so much time, the result is the same. Certainly a square interior is "more efficient" than a rectangular one, but in-practice I would be surprised to learn you were dissatisfied with the unit's performance. Unless you load them improperly or the machine itself isn't working right, everything in there is going to get clean just fine. I would relax about that.

What I'd focus on would be whether or not the smaller machine is big enough for you and whether or not it's quiet enough for you. You'll be living with it every day for many years. Those would be the most important issues IMHO.

I live in a household with only two people in it. Still can't quite imagine a smaller DW than the regular-sized one I have. It washes well but, more to the point, it's really more of a "dish closet" than a DW. It's a place where I can store my dirty stuff 'til I feel like turning it on. Other people have different opinions.

We stayed in a rental for 5 weeks last year, which had an 18" DW, and for two of us, plus occasional dinner guests, it was perfect. I think the key was that the rental place had Ikea plates: they're very flat and slender, so we were able to make the best use of the space because they could be loaded very closely. We were able to use the smaller space more efficiently and it worked well, with no unwashed areas.
If I needed extra space, I would certainly consider an 18" DW, provided I could also change my dishes to something similarly slender.

They load very well. They are optimized. If someone who doesn't have one poohpooh's the idea, disregard that person's poohpoohing. People who don't have something can often find a way to say something negative based on little or no real life hands-on knowledge. I've heard many friends say they wouldn't want drawers in their kitchen, but once they come over and see my all drawer kitchen, nobody makes any noise that is negative in any way. (I don't let my friends operate in my kitchen, so they might take a long long time to realize how good drawers are...) . Everyone I know who has an 18"w dishwasher is happy with it. In a small space, one alternative you might like to consider is the single 24"w dishdrawer.

Space was a major consideration when I was looking for a DW during my kitchen renovation. I didn't have one in my old kitchen either. I have a small galley layout. I didn't want to give up the extra 6" of cabinet space needed for a 24" DW. I absolutely love my 18" machine. It cleans very well. There are only 3 of us and it is large enough for our needs, even when we have guests. I don't use it everyday and don't use it to store dishes. Some of your decision will depend on how you envision using the DW. Take some of your dishes with you to test out in any machine you are considering to see how they fit. As with any DW, there is a learning curve to loading them efficiently. Hope this helps.

Thank you everyone that has posted. I appreciate your comments and feedback. I will take my dishes to the store to see how they load in both machines - I think that is a great idea.

Does anyone have experience with the 3rd tray on the top for cutlery instead of the cutlery basket where they stand up? I haven't seen it in person myself but am curious.

And, does anyone have the DW that has the matching cabinet door? Can you still open the machine if you don't put the cab door on right away? And, if I got a fully integrated 18 in dw, would I just order an 18 in cab door?

The trays are worth their weight in gold, a thousand times.

Opening a panel-ready DW without the door means you have to hold it down until you load a few dishes on the bottom tray while open. Then the weight of the dishes in the tray holds the door open. Also, it's a little bit dangerous in the first place, to have this unpaneled door, since it's spring-operated with no panel on it to give the expected weight for the spring. It will take an 18" panel. Read all the PDF's; do not rely on what friendly internet strangers write in any response.

Good to know, thanks davidrol

you may want to consider a single dishdrawer from Fisher Paykel. It will give you the 24" square and allow you to have a wide + tall drawer underneath it for the needed storage.

I recently replaced an 18" Frigidaire with a standard 24" and it's so much better. I put in the 18" 8 years ago when I bought the house and it was starting to rust and leak. When I went out to find a replacement, I discovered that Frigidaire had "re-designed" the 18" model and interior was now 20% smaller. The upper rack is ridiculous...maybe if you drink out of shot glasses, LOL. And all the brands (Frigidaire, GE, Whirlpool) were just re-branded versions of this machine. I didn't look at the expensive Euro brands as I didn't want to spend over $1K.

So I did what I should have done 8 years ago, which is remove another cabinet and put in a 24" dishwasher. The advice to avoid 18" dishwashers you mention is your first post is spot on.

From someone whose been there!

Ooooh, check out the below chat about 18" custom panels. It seems that is trickier and not as custom looking than with the 24" models.

Here is a link that might be useful: GE 18

i have an 18" panel ready that is being installed next week. I was able to attach 2 panels to match the 2 drawers next to the unit to simulate an upper drawer and lower pull-out. The thing I am looking forward to most is the cutlery tray!! I hate those baskets! My FP dish drawer baskets are always falling apart as I am carrying them to put the cutlery away!!

xand83, I checked out that post and that was one of the models I was considering (in my budget) but it doesn't have that fancy cutlery tray. Decisions, decisions.

Thank you everyone again for your posts.

Anyone regret having no dishwasher? If I can't squeeze one in somehow, I am sure I will be disappointed!

Life without DW? End of days...at least for me.