In another thread, someone mentioned the problem of enclosed Space Hulk fighting and the size of Tyranids. Perhaps the majority, or part of the fighting, could be conducted in the gun bays of a vessel. From what I have seen in White Dwarf, they are essentially cavernous places, with cannon on either side, much like the deck of an old sailing ship, but bigger. This would allow larger Tyranids to fight, as well as smaller ones in the corridors.
Been a fan of Warhammer, 40K and associated universes since I was six...and this is possibly one of the best looking HL2 mods I have seen in a while!
the whole reason for my registering was to put forth a couple of ideas, and keep track of your progress. A question, are you still having trouble/have abandoned the issue of spawns?