Grav Site Spawn Rate?

So I was gone about a week from Eve, only logging in to change training or attempt to help fuel a POS or two. You would think in that time we'd get at least one gravimetric site to spawn.

I logged in and started some heavy mining with 8 accounts, 6 Hulks, 1 Iteron V, and an Orca boosting. Cleaned all the ABCs out of a field and found myself low on time, so I decided to scan out my system and count the remaining sites. My count came out one short. I showed four sites on my list, but only three in system.

So really, there hadn't been a grav site spawn since I pretty much bought the wormhole, over a month ago.

Sure, we haven't attempted to clear the hole out or anything, but I've been knocking a grav site or two off each week we've been living here. We've still got 12 or more ladar sites sitting there. Makes you wonder if there's some sort of site cap for the wormhole constellation you belong to, and if you let a large number of the other sites build up, sites of another kind won't spawn.

It's just a guess, and probably not even close, but no grav sites in over a month seems kind of odd. Guess I'll do some gas harvesting and see what happens there. I do always have a second C2 wormhole to exploit, so it's not a huge problem.