I don't know if it is purely based on upvotes but what I can say for my account is that on average I used to get significantly less then one karma point per upvote. When I watched the upvote counter on the individual item[1] and compared it with my karma increase a view years ago it was pretty consistent at 0.5.

Back then I shrugged this of as effect of the voting ring detector but it left me wondering: can the false positive rate be so high and so consistent ... IDK. Needless to say that I never participated in a voting ring and I'm not that well connected that many upvotes should be from the same people.

An alternative explanation that crossed my mind was if it could depend on the story/comment ratio because back at the time I submitted much more stories than I wrote comments. I did this with good intentions, I often like to read what other think even if I don't get involved in the discussion, but I could understand if a platform incentivized a healthy ratio of submissions and discussion.

[1] I can't remember if this was true for stories or comment but I think I could only see it for one type of submission.