From what I have seen, my impression is that fungoids spawned by the pool are a special case. They seem to grow stronger (or more experienced) very quickly, regardless of how many of them you killed. I don't think this is the überjackal effect you are seeing.
By the way, I once had an altar nearby the fungoid pool, that was pretty awesome. It allowed me to exploit the mechanic for lots of piety - although it was still dangerous, because of the paralyzing rays.
You steal a scroll labelled HITME. The orc hits you.