Lets think on this ...
Pellets can't take as much "squeezing down" as bullets undergo during shooting. Pressures in the guns are just so much less that it robs a lot of energy trying to extrude the pellet into the rifling. So that's one problem with pellets that are too large. By the same token, pressures being so much less in an AG you can hardly afford to shoot a pellet that does not seal the bore (never mind how badly they will shoot).
Now with that problem in mind consider that a spring rifle generates a lot of heat in the chamber at the moment of firing while a PCP generates a lot of cooling in the chamber at that time. I have never seen a comparison of the pressures generated by my suspicion is that spring rifles generate higher pressures than PCPs at the moment when the pellet is being forced into the bore by the expanding gasses. I have no evidence for this, it is my suspicion.
A thin skirt will likely more readily form a good seal for the gasses pushing the pellet down the bore. A thicker skirt may well need to be forced into the bore with a tool before the shot (in the case of springers) or require more cocking effort in the case of magazine fed rifles. The same would also be true of softer vs harder alloys.
So it is complicated, and worse than that I am no authority, I'm just some clown pretending I have a clue.
My experience tells me that I have the best luck shooting larger diameter pellets made of softer lead with thinner skirts. It also suggests to me that the assumptions I have made above are true. I usually start by finding a pellet weight that shoots well in my rifle and then dial in head size. First figure out the weight the gun likes to shoot (and with PCPs that's going to vary more than with springers). Then figure out which head size works best in your rifle. I usually start with the largest and buy 4 tins in that pellet which shot best in the first part of testing. As soon as I find a pellet that meets what I expect from the rifle, I buy a minimum of 4 tins in that head size.
Good luck.