I make a variety of moderators from slim 25mm diameter 140mm long ones to 220mm 35mm diameter reflex back vented silencers and including a swift stumpy clone that I have tried (30mm by 140mm) on my raider that is quite good. Suppression is largely about silencer volume so more compact ones are generally not as quiet as larger ones. I do not rate the Belita even given its small size.

To reduce the impact on overall length reflex silencers can help. Again, generally, a reflex silencer will be quieter than a non-reflex standard type that extends the same distance in front of the muzzle but will not be as quiet as a silencer of the same length that is all in front of the muzzle (hope that makes sense!).

Making something as effective as an HW is not too difficult.