If you look at the map (https://locations.wafflehouse.com) they seem to avoid the central part of Houston though, roughly anything inside Beltway 8. Generally they have locations in the suburbs of big cities but not in the big cities themselves. Except Atlanta, as has already been pointed out.
(Disclaimer: I have never been to Houston except to change planes in its airport.)
(Disclaimer: I have never been to Houston except to change planes in its airport.)