The mats I'm using are designed to be fitted before grippers. The gripper risers go beneath the grippers so it wouldn't really work to install the grippers first (well you could put down the risers then the grippers then the mats I guess but you'd end up with the same gap in the end). https://www.soundproofingstore.co.uk/soundmat-3-plus
Why will you have a gap? The gripper riser is 30mm wide. Your gripper rod is 25mm wide. That leaves a 5mm gap to tuck the carpet? Sent from my iPhone using Tapatalk
You put the risers round the edge then for the matts up to the risers then fit the gripper Sent from my iPhone using Tapatalk
Looking at that site there shouldn’t be a gap. However it also looks like you would have to tweak it to get a correct gap for the carpet to be tucked into...
I guess that depends on how wide a gap you're leaving at the edge. The gripper risers are actually a bit wider than 30mm.