There IS a split if there are enough participants.
I'm not sure if there can be more than one split (given MORE people)

But the thing is, if there aren't enough people, there wont be a split, because there will be no one to fight half way through, that would be bad.

So thus far, everything is working just fine, except possibly the question of WHERE the split is WHEN there is one.

So what you are asking is more than one divisor.
Well, in any case it shouldn't be hard-bracketed by level, it should be something like this:

Let R be the number of registered player
Find D = R/45 (integer division, ergo remainder is discarded)
Find G = R/D (due to integer division, G can be anywhere between 45 and 89, inclusive)

The first G player, ordered by level and experience, goes into one group, then the next G go into another and so on, until D groups are formed.

Again, this would put between 45 and 89 players into each field, which is a reasonable amount. Thou obviously it can be adjusted by changing the "45", (If we call it C, the actual number in each field would be between C and 2*C-1, inclusive)

Granted, anything dynamic might be a bit harder to code than hard-bracketing one way or another, mostly due to potential resource allocation. But this would be ideal IMO.