Eurazhdarcho: a nightstalker?

Every new azhdarchid make the day a bit like christmas for me This new giant, Eurazhdarcho was found in Romania and is one of the smaller species (3m wingspan). But more interesting for me is that at the same time and at the same place another azhdarchid rule the land (and sky) Hatzegopteryx was on the other end of the size spectrum; a giant beast, tall as a giraffe, with 11 meters wingspan.
And they were not alone, in north america and it's the same thing: small azhdarchids and big life together (In asia maybe too, I believe I heard that asia had some footprints of giant pterosaurs...).
The questions are: why? and how?
How could such animals which are very similar- the beaks of small and big azhdarchids differ not much and the same holds for the body plan- live together. They could have hunt prey of a different size- Hatzegopteryx could hunt even middle sized dinosaurs- but I want to show here another possibility of how they could coexist.
I notice that some smaller herons are nocturnal or crepuscular (night heron or boat-billed heron etc.), big species instead are mostly diurnal (grey heron, great egret etc.). These animals aren't specialized on that daytime, some are actual very variable, but they have a daytime they prefer.
I imagine that smaller azhdarchids might have had a similar livestyle. Bigger azhdarchids, like Hatzegopteryx and Quetzalcoatlus, would have hunt big diurnal prey and the smaller species feet the small mostly nocturnal/crepuscular prey, like mammals and amphibians.

Well, I'm curious what you think about that


Edit: Sorry for the quality, I was a bit fast