Step 1: Align your sights properly.
Step 2: Pull the trigger without disrupting your sights.
He already admitted he is placing his finger on the trigger "properly."I do only have the tip of my finger on the trigger.
And step 2 requires pulling the trigger straight to the rear w/o any lateral force applied as the shot breaks. If a change in grip and/or finger placement facilitates that (and therefore Step 2 is achieved consistently), then it is certainly a valid solution.
He stated where he is putting his finger on the trigger. That's doesn't necessarily mean it's proper or he's meeting the goal above. The reason we read so many ideas about "where" is the perfect place is because it's going to be different for everyone, so long as they pull the trigger straight back.
Anecdotal evidence: Last summer I was working to improve accuracy w/ my ipsc open gun. While shooting 75 yd groups and 75 yd bill drills, I found I could tighten my groups significantly w/ a very minor change in finger placement. At 1/10th that distance it's "negligable," but the results didn't lie.
It's reasonable to say that you can get "adequate" accuracy especially for short-range high-speed/stress shooting w/o perfect trigger placement. And as experienced is gained it becomes easier to adapt the mechanics to pulling the trigger straight back and not disturbing the sights. But it's a crawl-walk-run thing. And I don't think that means the fundamentals can be totally ignored.
This isn't to say that trigger placement is definitely the problem. Could be lots of things. But I can't dismiss it. In fact, it seems like a reasonable starting point to help him learn to accomplish Step 2.
-rvb