Personally, I would not cut it and use the 12"x12" tile.
I have (2) meat probes and placed (1) towards the front on the right side, and the other to the back, on the right side. When I fired up My MES, without the tile, the back was 30* higher and the front was 20* higher, than the rest of the box.
The temp in the back and front right are virtually the same with the 12'x12' tile installed as the rest of the box.
I'm not an engineer, but I would guess the tile deflects the heat and causes the heat to circulate, rather than rise directly to the exhaust vent.