edit: just went back up and blew up one of the top pics. looks like there's no external shield on the charging handle. hmm... might explain where the gas is escaping. guess you could go to an adjustable gas block and shut it off when you slide the can on, but that sorta defeats the purpose. then you've basically got a fancy-looking bolt gun.
With an adjustable gas block you shouldn't have to turn it into a bolt gun for suppressed, just adjust the gas block until you get the least amount of gas needed to cycle the BCG when suppressed. When I switched all of my DI guns over to suppressed setups I put an adjustable gas block and the quick mount muzzle device on them. I then took them out and put one round in the mag and loaded it up. Fired it if the BCG locked back I turned the gas down and did it again until it did not lock back. Once I got to that point I turned the gas up one notch made sure I got the BCG to lock back and called it good. took me about 4 shots if I remember correctly. I don't remember getting any blowback in my face while doing this testing. I also am running just regular charging handles in my uppers so no special gasbuster handles for me.
I should have some free time soon so I will go shoot the guns supressed and see if I notice any gas blowback on them and will let you know.