EDIT: Scope transparency is bannable in RGL, do not utilize STRANGLE_PICMIP values which cause scope transparency(further testing from Zesty shows it depends on your setup. Mine was tested with a 5700XT) STRANGLE_PICMIP=9 to 17 when playing in RGL, and they probably fuck too much shit up anyways to be worthwhile, so probably don't use them in general. https://docs.google.com/document/d/1jfp2o6X4m0zdrX50kZ5YNsrvBANqxfDb-nEsRBb1wh0/view Section 1003.3 covers explicitly disallowed mods.
STRANGLE_PICMIP ranges causing this issue on my setup with a 5700XT and mesa are STRANGLE_PICMIP=9 to 17. They aren't generally advantageous due to some warping caused that makes where you're shooting somewhat inaccurate anyways, so probably don't use those settings regardless. Using PICMIP levels outside of your problem ranges should be fine, just check your rifle in a pub first.
As an update, I tried a few things and some undesirable results came out.
STRANGLE_PICMIP=9 through STRANGLE_PICMIP=17 remove the black outside of the scope, however they also cause weird warping and ghosting of whatever is in the scope, so you're not even necessarily looking at an accurate image.
STRANGLE_PICMIP=9 seems to be the least extreme and not quite decent for normal use(note the blue dot is repeated down and to the right even at this low of a picmip value. It gets worse later, but I believe this is where the actual shot goes.)
https://cdn.discordapp.com/attachments/156968469823356928/703438461754933289/2020-04-24-215156.png
STRANGLE_PICMIP=11 brings back the scope zone and provides an odd distortion at the edges
https://cdn.discordapp.com/attachments/156968469823356928/703439291832991784/2020-04-24-215621.png
however, after a bit of time it does this:
https://cdn.discordapp.com/attachments/156968469823356928/703439914561437756/2020-04-24-215840.png
This effect gets nominally worse up until PICMIP 17 and then stops entirely at PICMIP 18 in my testing. In theory if someone could get used to the warping, it could be advantageous, but that also requires getting used to some pretty bad warping that I would expect is a massive issue at long distances. My personal choice is that when you go past PICMIP 3 you go big and go to PICMIP 50 or so which prevents some fences from rendering and makes weapons and playermodels a solid color on top of providing an effect similar to flat textures. It also brings the scope back to a more pixelated on the edges normal, meaning you actually shoot where you point again.
Here is PICMIP=50
Scoped
https://cdn.discordapp.com/attachments/703607334886309979/703607369761947689/2020-04-25-090326.png
Playermodels and weapons
https://cdn.discordapp.com/attachments/703607334886309979/703607408714448916/2020-04-25-090322.png
The way libstrangle handles picmip is a bit weird, so at high picmips you may also see some abnormality in menus.
Edit: note this also messes with the heavy muzzle flash and makes the zone lights cover huges. Lights are still transparent, but the muzzle flash of enemy heavies may be annoying.