There's a small, maybe 1/2 inch, gap between my concrete backerboard underlayment and the bottom of my drywall. I want to install Ditra waterproofing (mat plus Kerdi seal tape). For waterproofing the outside perimeter, I'm supposed to apply thinset to the floor and wall 2 inches in each direction, and then stick on the Kerdi tape. However, how do I deal with this vertical gap between underlayment and drywall bottom? Would it be silly to fill it with drywall compound and mimic the drywall panel being flush with the underlayment? Should I leave it alone as it will be covered up by baseboard later?