I have 12x12 field tile and a strip of accent that‘s about 2 high. Everything I‘ve read says that you want to have the accent at eye level, which makes sense to me. Judging for myself, it LOOKS best at eye level. If I place it at eye level, I wind up with a full 12x12 tile above it, or at least, a 12 space above it. So going down to the tub, I would have a 2 1/2 cut tile at the bottom, right above the tub.Everything I have read also says that you want to have the cut tiles at the top and bottom symmetrical.
Run the full tile as the first course at the tub and the accent tile will be close enough to eye level to look good.
Provided the tub is fairly level, start a full tile at the bottom and work up. Tile will look fine at a 5 or six foot level ( I prefer 5 ft.) Not every one has the same eye level so the strip will be fine. The tub surround will be a bit different too so what I suggest is measuring on the tub wall the tile heights and stand back and look at it. Use a pc of tape the approx width of the strip and tape it or draw it on the tub wall s prior to tiling. Will give you a better idea. Also take into account any fixtures you may put in such as a shampoo/soap shelf. Any questions you can e mail me through my avatar and check my qualifications there. I ve also have down 100s of tub surrounds. GL