Potential bug re M1 Skin

I tested out the damage rates of the M136 launcher and all tank ammo types in a custom portal mode recently. The stats I discovered were similar to what Youtubers posted about in previous months, but I found an oddity and want to know if others have experienced this as well (and if not, whether they could replicate it). The phantom edition skin seems to have a bug in-which an M136 shot that hits the side of the turret closest to the rear will do 650-750 damage, while on the default skin it will only do 350. 

Has anyone else experienced this? Devs, is this a known issue?