This doesn’t feel stupid for me. If the desired beam is diffused, or if the optic is designed to produce a diffused beam, focus and centering isn’t very critical, but if the desired beam needs to be as sharp as possible, and the optics doesn’t have mounting posts or the correct footprint molding, or if we can’t use the casing that the generic tir optics usually arrive then we need to have some kind of gasket to aid in centering and focusing. “Improper” optics with improperly sized holes can also be used with such gaskets. When I tried tir optics sitting in the LED PCB it always yielded bad results, and the solution was to use a gasket that happened to be compatible, or to custom make some kind of gasket, like this:
There’s not a standard solution for tir gaskets, so every project needs a custom solution, not always necessary but it is necessary to always get optimal results.