It isn't specifically written in the law, but my interpretation is "yes."
The law states is shortest firing form. If you can remove it, it will still fire, therefore too short.
Just last year there were multiple PD's who were removing muzzle devices before measuring these guns, and confiscating/not registering any that were too short. Silver solder, tack welds or a pin fixed those issues.
This is only a problem with the AK's that fold directly at the end of the receiver. The Bulgarian triangle folders, the full size folder listed above, underfolders and the AMD65 because it is 16" to the end of the muzzle device.
The rear trunion that sticks out about an inch is what saves the other types of folding guns, even sans muzzle brake. Wire folders, tapco, etc.