Pointed out for general consumption, because Giuseppe probably knows all this.
When raising the gunsight by X amount, in the cockpit's hier.him it's necessary, of course, to similarly raise the reticle mask mesh. While not absolutely necessary to do so also for the reticle mesh in hier.him, it's wise (if not good form) to raise it equally. This ensures that the bullet stream will not become offset (provided things originally were properly aligned.)
If our game placed the reticle very far ahead of the plane, say, 100m, such tweaks to sight placement would not require to move the reticle. But because the reticles for our planes are typically located approximately 10m (1,000cm) ahead of the pilot, a change in sight placement of 1cm induces an offset of about 1/1,000, or 1 mil. 5cm would be 5 mils. Not particularly notable offsets, but worthwhile to avoid.
Now, some 'pits have the reticle nearer than 10m--down to about 8-ish, as I recall--and so an offset would result in a somewhat larger line-of-sight departure in mils.
And of course, a suitable raising of the PoV is a good thing to do as well.
I started doing this kind of thing for myself years ago... Some of the old stock sight placements were horribly low, presumably to 'hide' the cowling (and wing) gaps. The old MiG-3 was a particularly good example of a too-low sight.