I have an IG Prestige MP as well and I can definitely agree that it has a very small sweet spot. I've never really realized it as much until I had a 1.5 hour hitting session last night with a new 2013 Babolat APD. That thing has a HUGE sweetspot. Not once did I mis-hit the ball. All shots felt very solid and well-connected to the racquet. It was a nice vacation from "small sweet-spot-ville".
All I can say is the Prestige is an advanced player's racquet that's designed for people who have very good hand-eye coordination. Same with the BLX 90 that Federer uses. It takes more skill to wield those sticks consistently for an entire 2 hour match and live to tell the tale.
It's not the cap grommets, either. There isn't anything special about them, only that they add more weight to the hoop (which is their purpose).
Also, 52 lbs with a multi? that must be rather powerful. Honestly, you should be stringing that thing no less than 56 or 58 lbs with a soft, powerful multi such as RIP control. I think you may find better stability with your shots.
I don't use multis in my Prestige, I use poly so I can get away with stringing @ lower tensions. I understand you may have arm issues, but that's a really soft frame. If you still have arm issues with a soft multi @ 58 lbs on a 62 RA racquet, then you perhaps should see a doctor. It doesn't get much softer than that.
OR, your stroke could be off. What's your grip? SW? E? W? Perhaps post a vid of yourself hitting in the Tips section.