The skill selected is probably (at least partially) random, however the size of the drop probably isn't. I've never see a double drop in a skill below 10-11 (for reasonably old players, like 34-36). Of course it does depend on sublevels too.
I think the impression that higher level skills are more likely to drop, may be simply due to larger drops for higher level skills.
Last edited by Lemonshine at 5/11/2015 10:14:12 AM