In reply to Colin Dyer:
yes, my pinkie too is a full joint shorter than my other fingers, which it makes it impossible to use it in any grip other than full crimp without twisting my wrist at un-natural angle.
Someone once said " I couldn't help but notice and wondered why you are using a 3 finger half crimp on the campus board" I waved my hands at him and pointed out my short pinkies, he nodded in understanding and didn't say a word more.
My theory is that short pinkies give me an advantage on 1 and 2 finger pockets because I am only 1/3 and 1/2 as many fingers as usual so am stronger compared to someone whose normal grip is 4 fingered and therefore is only 1/4 and 1/3 as strong on those pockets.
I do find that with short pinkies, they get used so rarely that they are much weaker than the other fingers and prone to tweaking on the few occasions when the hold shape allows it to fit.
I have considered training my pinky on its own to get it closer to the strength of the other fingers, but mono pinky holds are pretty rare.