I’m installing the 38” x 76” Schluter linear drain shower tray. I purchased the 35-7/16” linear drain which will give about 1.5” on each side which I’m a bit worried about how to fit tile into that small gap. Should I go with the 31-1/2” linear drain or even the 23-5/8”? With the smaller sizes I’d just have to make sure it’s sloped inward on each side. The drain will be up against the wall.
I don't think that there is a single answer to this question. It comes down to a combination of your shower dimensions, the tile that you are using, and user preference.
They also make a linear drain that you can cut down to fit from 10 inches up to 8 feet called Kerdi-line-vario (PDF).