This is something I have experience with, both from my benchrest .22 shooting and actually trying stuff with SKSs.
The short answer is.... there is no one answer.
When you fire a bullet, the barrel flexes up and down, in a motion similar to waves on the ocean. And since it's flexing up and down, that means the muzzle end where the bullet comes out as well. So sometimes the end of the barrel is flexing up and sometimes it's flexing down.
With that said... where the barrel is at the point of bullet exit, is what dictates where the bullet will go. Sometimes bias upward, sometimes bias downward. Barrel TUNING, is when you makes changes on the gun, to make the bullet exit the barrel on the same exact "wave" every time. So if your bullet leaves the barrel on the up wave of the muzzle every time, you get tighter groups and better accuracy. Barrel tuning is generally achieved with a barrel tuner. This is a device that goes onto the end of the barrel and alters the wave pattern to be consistent. Some tuners are adjustable, and some are solid, calculated of complex formulas. Barrel tuning is definitely a science.
But when it comes down to it, a barrel tuner is simply a weighted device on the end of the barrel. So, ANYTHING hanging off the muzzle can change the dynamic. An extended bayo, a muzzle brake, a silencer....anything can affect it. Sometimes it helps, and sometimes it hurts. In the case of the SKS, I have had my groups shrink in half with the bayo extended on some guns, and grow twice the size on others.
And, there are other variables too that affect tuning. Especially ammo. The pressure wave from the explosion of firing a round is what transmits through the barrel. And the weight of the bullet itself will change at what point it exits the muzzle too. This will change with every shot when using run of the mill ammo. Because powder charges and bullet weights are not exact from round to round. That's why hard core target shooters use "match ammo". Match ammo is ammo where every round is made virtually identical for maximum consistency.
So what does this all mean? It means every gun will be different. There's no definitive answer. You just have to do some trial and error with each specific gun you have and see how it reacts.