That is fine for a tttf in sun. In my experience, 4" is starting to push it in shady locations and the grass tends to get a little floppy between mowings.

I think TTTF does well mowed at that height (I'll defer to Bill's wisdom on the shady areas; I don't have a lot of shade and the altitude makes partially shaded areas act like sunny areas elsewhere).

It's very important to keep the blade sharp since TTTF is prone to tearing.

There's some truth to the claim that taller grass will grow deeper roots, but there's not a 1-1 relationship to it and there's a limit to its effectiveness. Taller grass can grow deeper roots for a couple of reasons. For one thing, if it's mowed short, the grass is always expending its energy repairing the damage. If it's mowed tall, it has a chance to use some of its energy to grow roots. Taller grass also helps shade the soil, making it cooler and keeping the roots from shriveling (it doesn't really shrivel, but . . . ).

I too have TTTF. I cut it to 3 inches, and I have the same issues with it not returning to it's upright appearance as you do. I think cutting to 4 inches for TTTF is too long for a few reasons. First of all it raises the height of the node where the blade meets the stem. This makes the lawn less green, and stemmier when it's cut. If you mow to 4 inches, then that means you are letting the grass get to between 5 and 6 inches. In addition to looking messy and floppy, this also makes the environment for lawn disease better, as the grass will be continually wet. Also a long period of rain in the summer can potentially cause the grass to get to over six inches if it starts at 4+ inches, which isn't a good thing. Most TTTF growers say you should mow at 2-3 inches on the bag, and that's good enough for me. Here's a good link to an overview of how grass is affected by mowing heights, fertilizer, temperature, and other factors. Hope this helps.

http://www.purdue.edu/envirosoft/lawn/src/physiology.htm

tiemco, can one cut it at 1.75inch? I still see stems when cutting at 2.5inch. If I can, how should I go about doing this? Is it too late in the season or will it damage by cutting too close? Right now, the grass is probably over 3inches.

Technically yes, you can, but that is under very managed conditions, and I wouldn't recommend it. Plus I think you misunderstood me. You cut AT a certain height. You cut it TO the lower height. If you see stemminess when the grass is 2.5 inches, then you are going to see more at 1.75 inches. Plus at that height it is very stressful on the grass. Usually you raise the height of your mower during summer to the highest recommended setting for your grass type. I would probably raise your mower to 3 inches (assuming you have TTTF) and mow the lawn when it reaches about 4 inches. Remember you only want to remove one third of the blade height when you mow, so if your grass is about three inches now, the lowest you should cut it is 2 inches.

At first I thought the lawn was KBG from all the seeding going on but upon reading your post, I went to check closer and saw tttf mixed in. So it seems I have a mix.

Seeding KBG is unsightly, worse than having clovers. Will cutting higher encourage more KBG to seed?

I don't know enough about KBG seeding to know for sure but I would say probably not. If it seeds at 2 inches it will probably seed about the same at 3 inches. It will probably be less noticeable when the grass is higher. I suspect it will be gone in a few weeks anyway, so just be glad it's not poa annua.