Stevio

I've got a set of OPS Quattro SMG Pocket / Panel pouches for my mp7, which also fits mp5 mags. Comes with either bungee closure or flaps, and inside you can adjust the height for a better fit. I believe they also do them in doubles too.

I'm not sure if this 100% fitted your criteria but I picked up From this guy https://cults3d.com/en/3d-model/game/airsoft-micro-grenade-impact-cap-gun-ring-sound-grenade-meteorite-meteor-lite-e-fulcrumairsoft He sells complete ones on ebay. My local was happy for me to field it as it's not nearly as loud is a .209 primer bfg. Super small, fits in a 40mm pouch. Only downside is if it gets wet they don't trigger For the price it might be worth a try

Plus Araments make one with adjustable timing https://www.pulsearmaments.com/product-page/Gen2-B1-209 They're a little on the expensive side and while slimmer they're are probably not much smaller overall. There doesn't seem to be many timed bfgs on the market. I personally have an oshiboom impact and as you said they don't work very well outside of the hardest of surfaces. I've also got a SWAT BFG which i'm pretty sure is a clone/improvment? of the dynatex

Why is everything always listed as "never used" or "used a couple times". Apparently nobody ever skrims their kit anymore