[olddog]

I suspect they intended for you to use the red gasket as a template, and cut the whole to match. I cannot say for sure that is correct. I would under cut it, unless I needed all the clearance.

I can say on my car no force would go to the base plate unless the bearing in it froze up.

PS
Those tabs may be designed to stop you from over tightening and cracking the glass. I assume there is a plate (that is not shown in the picture) that goes under the hood. That plate likely will hit the tabs and prevent crushing the glass too far. That would also let you tighten the bolts more, so they do not come loose.