I always ask if they have window MCE when i go standby (3-5x a year). In each case i can remember I've been given the best seat possible. Furthest to the front non-middle. However i do notice that they print all boarding passes out when they are clearing the list. So if i was say
#6 but very near the gate and go up first , and ask for something specific thy could change it. Never happened, but possible i guess.