Finally got myself a Burris FastFire II for my FNP-45 Tactical. This is my first MRDS, and have a quick question on mounting. It says I need to mount the gasket plate under the sight for waterproofing/resistance. I Assume this to be that gasket plate: IF so, then the kit also includes a thicker firmer "gasket plate", which to me is more like a shim. IS it a MOA shim (for elevation adjustments), or is it the "gasket" plate?