Just an "uneducated" idea from a non gunsmith.

But maybe have a look at the rear wedge. Is it pushed too far to create too much pressure to open up the barrels? The wedge is moved forwards or backwards to open up the barrel gap or decrease it at the back.

It MIGHT be pushing too hard at the rear of the barrels and is causing that large gap at the muzzle?

Loosening the screw holding the rear wedge, and reducing the pressure from the wedge, see it the barrel at the muzzle drops back down into the "saddle"?

I do think the barrel should not be "free floating" in the "saddle".

Have a look in the Valmet manuals provided on these forums and see if anything in those help you work it out. I will post a link once I look for the thread.