The very top of the post is slope cut.  Is there a reason for that?  Also, the whole thing isn't cut to .05, only two sides and the rest is normal width.  

mine too, it looked weird like that. I thought the whole thing would be thinner.

Quoted: The very top of the post is slope cut.  Is there a reason for that?  Also, the whole thing isn't cut to .05, only two sides and the rest is normal width.

It is tapered and only one side of the side is designed to be facing the shooter . . . it's sort of like a directionally treaded tire (it has to be pointing a certain way to work properly).  This gives the sharpest image of your FSP for high-accuracy NM shooting.

High side towards the shooter.  NM sights are one turn affairs up front.

Quoted: High side towards the shooter.  NM sights are one turn affairs up front.

So fine tuning the elevation has to be done with the rear sight?

Quoted: The very top of the post is slope cut.  Is there a reason for that?  Also, the whole thing isn't cut to .05, only two sides and the rest is normal width.

If you are truly Zen with the rifle and the sight, the sloping edge prevents the glare/"false" surface of the top of the post from throwing your aim off.  With a level post, there might be a glare or the top of the post might be visible if the sight post is not truly vertical or if your eye is lsightly off.
To most shooters this has almost zero effect, but to true HP and long distance shooters it does make a difference.
The idea behind adjusting posts like that is that you get it as close above/below BZO, and then file down the top.  Very carefully.  Or if you don't trust that, just note where the hold is for given ranges and apply that.
Or as you said apply rear sight adjustments.

Quoted: Quoted: High side towards the shooter.  NM sights are one turn affairs up front. So fine tuning the elevation has to be done with the rear sight?

Roger that.