Hi Dan,
I have two questions:
1. Are you using factory cartridges or range reloads?
2. Finger joint or pad on the trigger? (Waitone has already hinted at this angle)
At ranges about 30 feet and beyond, the trajectory dip of weak reloads can get really pronounced. The execrable reloads I had to deal with in the past produced a dip of nearly 10 whole inches at that range.
I changed my handgrip on the advice of an instructor and my accuracy suffered: overengaging the grip and trigger led to a slightly left and low POI, unless the weak hand worked hard to prevent it.
The effect was particularly pronounced in Weaver for me, less so in Isosceles, and bugged me no end until I reverted to my natural grip.
hth somehow,
horge