We encountered something similiar with about a 2" on the end of one wall, however we were going with the tile vertical and stacked above one another. We had a professional, who laid our tile in the majority of our house come over to answer a question we had about the window in the shower and before Hubs could even ask him about that, he looked at Hubs layout and said, "you never have that small of tile on the end of a wall." That and the issue of the window had us re evaluating everything. He wanted us to bricklay the tile (12x24, like yours with 1/8 grout line), as he said that was the way to solve any issues. That wasn't the look I wanted so we started over and Hubs, with the help of some people on here, finally came up with a solution. We ended up going horizontal but matching grout lines. Before any tile is laid though, make sure your tile is actually 12x24. Ours was actually a little less than 12 and a little less than 24. That little bit adds up when you only want 1/8" grout line and you are dealing with a small bit on the end of a wall. I didn't want bricklay pattern as I wanted a flow from the floor to the shower since we are having a 39" glass panel and 30" glass door. So far, it has taken hubs a couple of weeks to cut and lay the tile himself, but all the grout lines are even and we are down to finishing the bullnose and the floor. If you are wanting the bricklay pattern, then your tile guy's solution might work. Try drawing it out on the computer and see what it looks like. That's what Hubs did and it helped me see what he was wanting to do, or draw it out on the shower wall itself.

Attaching picture of 12x24 tile. Note the patten repeated every 3 rows. Going in the same direction of wood floor in other room (long way of kitchen). Note 3rd picture showing hall. If you put the short way of the room look at the cuts. Will you have a lot of cuts those lose the reason for the 12x24 tile. I think if you want see 5 or more or more full tiles per row why do the 12x24 Below is example of how it looks in the hall

I have to laugh with the "red guard contractors". Yeah using membranes and mixing and matching different name brands and components to do a simple shower is the way to go. The more components you add the more to fail. Schluter saved everyone with their barrage of internet advertising. Heavy tile require a strong base. Your best bet would be simple roofing felt and some floated walls. This entire waterproofing deal is just out of control on here. One more time, the entire issue was when green board was being sold as or though to be waterproof. Tiling was done right over the gypsum board and when water intrusion happened the board crumbled and mold formed. Funny thing is do you know how many showers are still being used exactly like that with zero issue? There isn't a tile person incl myself who did not do showers like that back then. I had one in my own home that was going on 20 plus years without an issue as the caulk and grout was always kept up. Do most people even realize these membranes and some roll on waterproofing are still designed to be used on gypsum board. thats their entire purpose not for cement board although of course they can be used on them. Pick a tile that works for your layout. What you are seeing is what happen when these offshore Co's produce tile not taking into account normal US shower or tub sizing. Heck, they can be floor tiles?

Do you have a box of the tiles? You could lay some on the floor and just see what is visually appealing to you. We did this, and decided to lay them left to right (not door to wall) because it is was just more comfortable to look at. If you lay out a couple of rows of tile one way, and then the other way, you will have your answer. When you do it, cup your hands around you eyes (like race horse blinders), so that you are not distracted by the rest of the blank room. Look at it one way, then switch it and look at it the other way. Whichever way looks better to you is the way to go. And just for the record, I like having a toilet room too. People have strong opinions on that subject.