fiber optic sight brightness

Ok, so not really CZ specific, but I put Dawson precision fiber optic sights on my PCR, and have a question about rod replacement. I figure some of you are running fiber sights, and might have some insight.
I'm looking for any advice on how to make sure I'm getting the most light transmission when I install new rods. It's a pretty basic process, which I have no issue with, but I still have a question. When I replace a rod (which I've been doing pretty regularly as I figure out what color(s) work best for me), part of the install involves melting a bit of the tip so it mushrooms out, and holds in place. It seems like when I do this, the amount of light being transmitted deceases dramatically, particularly when compared to a raw exposed end of cut rod. I understand there will be some change in transmission of light, but am hoping to maximize the brightness of the rod after install. I have a sense I could be improving my process to help this. Maybe temp of flame, proximity, size of bulb? Other variables I should consider?