From Magpul Tech Support.
"Thank you for contacting us. With the grip because it was installed on an AR10 platform that kind of gap will be normal with any of our AR15/M4 grips, for AR10s that run an SR25 back strap cutout we make the MIAD 1.1 type 2 as that has the taller beaver tail to match the taller receiver that SR25 have."
My Reply.
Thank you for the info on the correct pistol grip. I've sent a link for that grip to S&W and hopefully future models of this weapon have the right grip installed.
https://www.magpul.com/products/miad®-gen-1-1-grip-kit-–-type-2