Hey nice rifle there...

The standing rear sight on this rifle is flat across, as are the two flip leaves.
The notches in all three are simply what seem to be hammer strike witness notches. The front sight is a square block on a dovetail. I have rifles with express sights like you have there, the standing main blade being a pronounced 'V' shape like the one you have pictured. I agree with you, that arrangement with a bead type front sight is a wonderful setup.
I have seen new old stock mid nineteenth century multi-blade sights like the one on my gun with the same arrangement of witness strikes as what would seem to be 'starts' for filing the sights to regulation height. I've seen numerous period sights on guns that obviously had been working, running guns where like the blades on your sight had been opened up to some extent either via files or gravers to get them to the proper sight picture for the given range the sight would be used at.
I just think this particular rifle never got it's sights tuned to whomever would have been shooting it.
The breechfaces have no peening from cartridges hitting them, no powder burning at the firing pin slots or on the breechfaces, and it's clear that this gun hasn't had it's metal refinished. The bores are absolutely goregeous, the chambers perfect, the muzzle crowns crisp.
Perhaps tonight I'll photograph some more details of the rifle and post them to this or one of the other threads I've started on it in the past couple of weeks.

I had it and my Tolley out to shoot today, as it went I shot the Tolley quite a bit and only put two cartridges through this gun. The chronograph was on the fritz so I didn't bother working much with sixteen bore black powder double rifle load development today. I have a batch of brass in the works, and I want to do a stock bend before I do much more work at the bench with this gun.

--Tinker