Finger slips
Philip, what precisely do you mean by the "tip of the finger" and "too much finger"?
I agree with 9mm that this sounds like a grip problem. When setting up for a first shot, can the "wrong part of your finger" reach the trigger? If so, you might be unconciously repositoning your finger during recoil.
If not, the weapons must be shifting in your hand.
Go back to the fundamentals and check your grip technique. In particular, do you push forward a little with the shooting hand and apply a little counter pressure with the supporting hand wrapped firmly around the shooting hand? This technique should prevent the weapon from torquing to the right, which I assume is happening (assuming you are R handed).
Are the weapon's grips unusually smooth?
How about fit? Is it possible that your hand is in fact a little large for the grips you are using. If the "wrong part of the finger" CAN reach the trigger when holding normally, try this experiment: wrap a piece of (preferably bicycle - thinner than auto) inner tube around the grip (the amount used adjusted to prevent TOO much increase in grip size), and see if that makes a difference. Does it prevent the "wrong" part of your finger reaching the trigger? Does it prevent the shift when you shoot? The rubber should eliminate any slip of the grip in your hand too. This test should help tell you if 9mm's suggestion of changing grips would help.
I would try solving the problem with the lesser recoil 9mm first, not using +P ammo. With the ligher recoil it should be easier to analyze what is going on. Then check with the 45.
Of my 3 9mm semiautos, the Model 699 S&W with heavily checkered Pachmyr grips is VERY stable and only the correct part of my finger can ever reach the trigger. My Hi-point has rather slick grips, and holding it in my right hand, I can easily rotate it to the R with my left; also I can reach the trigger with my knuckle. However, I have no problem shooting. The small, unmodified Kel-Tec P11 is less stable in my 2-handed grip, but nowhere near to the the extent you describe, and I can fire a magazine with little problem.
Something I just checked with the Hi-Point is a two handed grip with the left forefinger hooked around the trigger guard, a practice that is frowned upon today, but which I can't get rid of (old dogs ...). I found that using this grip it is absolutely impossible for the weapon to twist to the right in my hand. This might cure your problem, but if it doesn't I'd think you are unconciously re-positioning your finger. If it's the latter, I would recommend fatter grips that prevent it (based on my S&W fit).
Of course every hand is differerent, and what works for me may not for you.
After you make some adjustment to correct the problem, you may have to be patient to regain your accuracy. On the other hand you may shoot better
I hope these ideas help. Let us know the results.
C