If Daedalus underestimates his English skills, then I might say he also does so for his tactical sense, since his advice merrors what I had been going to give, at least to a great degree.
The traditional way to play the Clans, and so most of the traditional Clan halo-mechs, matches speed, skill, and power in a combination that alows one to take and hold the stretegic innitive (not the dice rolls, but the perceptions of who's making who react to their tactics) and pumel their enemy into submission in the time and place of their chousing. But, this does infact require large maps. Sure, your Stormcrow can run rings around nearly any IS heavy (yes, I know about mechs like the Grand Dragon with the MASC) while still being able keep pace with top end slower mechs like the newer Marauders for power... but if its constrained by artifical map limitations, then that Marauder (and 60% of another mech) can easily enough courner it and take its speed and gunnery skill out of the equasion.
What the IS side wants more than anything is to make the game about power and armor, since the IS side will nearly always have more armor, and if they pick well more power. Small maps favor this greatly.
But, if you can't escape the small maps, you can always just pick top end units that offer a lot of poer and armor for their price (in BV, tons, C-Bills, whatever, it tends to be the same group of assualts and slow heavies). Oddly, its not top fight mechs as much as it is middle of the road ones (Dire Wolf Prime or B, Savage Coyote, the Nova Cat with all the silly ACs, and so on) that offer the best value, since you still get the armor of the top mech, but save on expensive (in BV terms) weapons. If you design your force cleverly, you can just go toe to toe, gun for gun with the IS and have a ghost of a chance, even on a small map, or in tight terrain that limits the movement and line of sight that moble forces crave.