As mentioned above, the middle of the pad on the tip of your finger *should* be where the trigger rests. However, it appears that folks that have larger hands usually end up w/the trigger resting in the first joint of the trigger finger or somewhere on that second pad. Hell, I'm a south paw so I do every thing wrong anyways!
If it works for you, it may be best to just stick w/ what you know.
I finally stepped up some w/ the addition of a First Samco (FOBUS) G-27 grip. I must say that it took me by surprise because the trigger feels weird having it's purchase w/ my trigger finger shifted due to the grip. As much as I like the G-27 grip, I keep hearing this echo, "MIAD, MIAD, MIAD".... I'll certainly be checking out the MIAD in the future. If I'd have heard about it before my G-27 purchase I'd have probably checked into it as it would appear folks here highly recommend it. The FOBUS grip puts the trigger just in front of the first joint for me as opposed to the middle of the pad. Perhaps the MIAD will give that little bit extra and allow my trigger finger to rest naturally in the middle of the pad. (Then I'll probably have to learn my trigger control for the AR15 all over again!)
It's also noteworthy that just because I've modified the grip to place the trigger more at the tip of my finger, I may just go back to using a standard A2 grip and having the trigger rest on my second TF pad. It's worked for over a decade, and as long as it works for me- that's all that really matters.
Sly