It has been my experience with CCMT, that I generally prefer shooting, noise, and mayhem. Searching around a large map for unseen enemies, although interesting at times, is not always fun.
Nevertheless, I settled on 600 meters (square) for each and every map. Each deployment tile is 24 meters square and there are 625 possible deployment tiles on each map.
CCMT also uses small team sizes for the good guys, and some larger teams for the bad guys. At 600 meters square for a map, vehicle combat is cramped, while infantry battles are just about right. Any increase in size, makes vehicle combat seem more realistic, but makes infantry combat seem pointless. Even with a 960 meter map (the largest size in CCMT), mounting into haltracks or trucks for infantry transport is tedius, and not very realistic either. So, I generally use mountable vehicles for heavy weapon platforms that can move.
Since vehicle combat can sometimes be very embarassing for the AI, I attempted to optimize map size for infantry combat.
@xe5 - Frontages must take terrain into consideration. In addition, the number of victory locations and their placement, may require not just frontage but a defense in depth as well. I find that a 600 meter map swallows up WW2 teams, but seems more practical for modern infantry equiped with longer range weapons.