I think there can only be 3 on the second floor? Anyway, this makes me wonder; Does the actual frequency of boss packs depend on the map? I know their location does, but I haven't heard anything specific about the number of boss packs.
As a random aside, can spawn location of packs determine how frequently they appear? A lot of the rarer packs on my map generally spawn tucked into corners (as opposed to in open areas) where they might not be able to be generated sometimes. (...or am I just delusional?)