seems reasonable to me. while we're at it, why not introduce a fourth type:
"remote"
as in "remotely activated" - which would make sense for the high explosive packs, wouldn't it?
the only reason not to use a remote detonator would be fear of interference with alien technology (as in "all hi-ex packs explode when nearing a UFO"), which would make sense as an excuse for not including this possibility if we don't want it, but I think I know some modders who would like the possibility