I'm not sure. If anything, the T-Grip should make the Magna grips feel larger and maybe a bit shorter. I don't know why your pinkie would be affected without seeing how. Maybe your hands are large as you suspect? (It's not installed upside-down, right?) If you use any other style of grips but Magnas, such as target or any of the aftermarket rubber grips, then a T-Grip is typically unnecessary, if not impossible to use. So there's alternatives in that direction.
I like my T-Grip because it helped keep my grip where I wanted during successive shots. Otherwise my hand tends to slide-up and wedge behind the trigger-guard, by the 5th or 6th round: My hands are average-sized but my fingers aren't very stout like some folks. And of course, I favor the classic Magna style grips.
Hope you get it sorted.