This is the info I got from Blaine at VLTOR when I asked him the difference between the VC-1 and VC-A2...
The shorter A2 model is not a Comp like the larger VC is. It's a flash hider. Designed from the outset as a flash hider to out perform the standard military A2 flash hider. The VC-A2 also uses the same external dimensions as the military A@ to allow for mounting of blank firing adaptors or flash hider mounted suppressors like the HALO or OMNI. The closed bottom helps reduce dust being kicked up in the prone position.