Muzzle Device Lengths

#1
I’ve noticed a trend towards shorter muzzle devices “for mounting purposes”. Recently DeadAir released a KeyMount Micro single-port brake. SiCo has had a single port ASR brake out for a while as well. Sig designed all their mount brakes as extremely short brakes when they started making silencers.

Is there a known minimum length a muzzle brake or flash hider needs to be in order to be effective? If not is there another reason to go for a full-sized option vs these smaller ones?
 
#2
Is there a known minimum length a muzzle brake or flash hider needs to be in order to be effective? If not is there another reason to go for a full-sized option vs these smaller ones?
What constitutes “effective”? And on what cartridge and barrel length? Lotta variables.
 
#3
If it will only be used as a suppressor mount, shorter and lighter is generally better. If you'll be shooting without, then longer is generally more effective. That said, a better design could be more effective at a shorter length.
 
#4
I should have been more specific. Let me try rephrasing to my specific case.

I have a Sandman-K and a Wolfman. The Wolfman requires a shorter mount (KeyMount Micro) due to the blast chamber length not accommodating a full length KeyMount Flash Hider or Brake. The Sandman-K is compatible with both the normal and micro KeyMounts. The Micro is only a single port brake vs their full size 3 port. Ideally if there is no discernible performance difference I’d default to all micro-brake mounts (lighter weight, more compatible, blah, blah, blah).

Here are the rifles I have in mind:

AR-15 with a 14.5” 556 barrel

AR-15 with a 9” 300Blk barrel

Bolt with a 16” 308win barrel