My sp36 pro has a ugly ring round the hotspot which really annoyed me. I tried to cover the whole lens with D-C-Fix, the result was a beautiful smooth beam profile. However it did cut back on the throw and lumens. So I placed little round cut outs of D-C-Fix directly over the LEDs which kept the throwie beam profile minus the big ugly ring.
Without D-C-Fix
With D-C-Fix
It seems to have the same amount of throw. I did try slightly smaller but than you have to be super precise with the placement.
I have done this with frosted scotch tape too with decent enough results. I always ended up taking off though, my mind never could get past the lost lumen factor.
It seems to have lost about 100 - 150 lumens out of 8000. The difference is negligible.
I to added DC Fix to my SP36 lh351d and the beam was very uniform but I could not get past the lost lumens either so removed it. I will have to give this a try. Thanks.