Hi rich i use the wedi trays in wet rooms......but it just down to choice.....
I also use schluters kerdi for tanking walls and floors....
To get the falls in the tray with largish tiles is to envelope them...this is cutting them from corner to corner as if you were cutting for diamond pattern...
just like this one i did with travertine....
Tiling the tray in mosaics is another easier option....
You will also need to check to see if you can accommodate the falls needed for the waste from the tray.
Also have a read of this thread it should help you as well....
wet rooms info...
good luck and let us know how you get on.....maybe a few pics would be nice to see.....