i also have a p99 AS and i have come to admire it's qualities so much,that my techniques have changed and been applied to every other gun i own.
it's trigger pull weight,smoothness(especially after the first couple of hundred rounds,now into thousands) and quick reset,is now what i measure against every other pistol(i started out long ago with DA/SA,stuck to it and i don't understand other peoples negative comments on "transition",..and prefer not to give up a sweet SA but prefer a first DA shot with no safety lever,especially when on my body).
anyway,i like using my trigger finger for dropping mags on the p99 and so what i have done is go back to almost all the pistols i already had and switched the mag button from left to right(as for a left handed shooter) and now buy new pistols where it allows me to do this(thankfully,most have this).
as a result of doing this and owning the awesome p99,i have come to a surprising revelation.some pistols,but not all,require that you totally disrupt your grip to drop a mag if the button is on the left side and you use your thumb.this is because of different grip sizes/shapes on different make/models.however,as a general rule,for me,i have found that switching over the button to the right,requires much less changing of my grip when using my trigger finger on all the different pistols i have(and suspect the same for any new ones i get in the future).it also helps,for safety reasons,that my trigger finger is doing only one thing,..it is either on the trigger itself,straight somewhere on the side off the trigger,or on the mag release.it can't do two things at once but with using your thumb to drop a mag,it is at least,at the very minimum,possible.
i thank the p99 for helping me in this regard and have also gone back,after getting used to it's trigger,and have done trigger jobs and/or,at minimum,changed out the hammer/main spring for a lighter but reliable ones. once you have drank from the stock p99 AS trigger goodness,you never want to go back.unfortunately,finding a reset just as good,is another matter but i usually settle.
i should also add,my index/trigger finger just moves slightly more to the rear to press on most other pistols but that doesn't matter,they're all in a slightly different position anyway.