It will only show an 8x8 on the 256 (although it will work).
TPV2 is made for 128s only, since that appears to be the ‘standard’ monome size nowadays.
Because of how things were mapped/conceived, scaling up is kind of weird. Ages ago I started trying to make a 128 version of TPV, so you would basically see two pages at once. I never finished it, but that was my solution to that problem.