I use washers that have a hole just big enough for the emitter (5 to 6mm).
I prefer fender washers which are large relative to the hole size. I have a selection I’ve gathered with various thicknesses. I’ve sanded them smooth them out and remove any burs.
Take your calipers to the hardware store and pick up a few. There is usually a range of thicknesses to you can find the right size washers in bulk, so you can pick and choose.
If you want a complete selection, take a feeler gauge set, and drill an appropriate size hole in the thicknesses you want.
Something like this:
Overkill? Yes.
But you would have an almost unlimited selection of thicknesses.
Still playing with the thickness some. Adding a layer of silicone works just as you would expect. I’ve increased the silicone thickness to get higher CCTs. It is hard to get a nice smooth beam this way. It is better to slice to the preferred thickness the first time so you have a nice flat surface.
FB