I’ve never carefully compared, but in my cell culture experience (quite a bit), adherence can very wildly across cell lines, and I’ve experienced times where cells appear to adhere less to the same slips in one experiment versus another, or even on one slip out of a set of multiple. Quite a few people will do a poly L-lysine coat of their cleaned glass coverslips to encourage adherence, some will use extracellular matrix components, just be aware that coating onto a protein matrix (collagen, fibronectin, a mix, or things like matrigel) can cause biological differences due to signaling…Good luck with your experiments.