Absolutley SOP - with a fixed height rear sight, shooting and trying various height front sights is the only way to zero the sights to the gun. Much the same for Express sights - the standing sight is zero'd the same way with different front sights, then the leaves are filed for longer ranges.

Not sure I understand the tunnel, except maybe for strength. If the hole closest to the shooter's eye isn't smaller than at the front, there can easily be too much glare with such a sight.

That rifle just shouts quality, doesn't it.