That's the bit we tend to forget - we sort out getting it to stand on the correct base, and then ranking up in a unit, and then... but if you worried about that every unit would have weapons held upright and so on.
The basic problem is that GW are still using the same base sizes as in 1984, but their models are twice the size!
Great idea for a BSB though! Do you play against Dark Elves a lot or is that a purely aesthetic choice? And what is the base model you have used for Calliste, I thought I'd seen every female vampire candidate but I don't recall that one.