I keep my Leopards under very different conditions than my Collareds. Leos are indeed nocturnal. They have very different behavior than Collareds and somewhat different natural environment. Leos don't need as much space. I would not recommend keeping them together. If you are trying to maximize space and want more lizards I would say add a few more Leos! I keep mine in 1.2 groups. A bigger tank could easily take 1.3 or even 1.4, but you gotta be careful that their breeding doesn't get out of hand with that many females in one tank.
I absolutely love my collareds, but I must say...they've been a LOT more work to keep them healthy compared to captive bred Leos. I don't think I'd do as well if they were in the same enclosure.
This is my big girl Bambi! She's a beauty but I don't think she would want to live with a bunch of spirited Collareds.

