I had to have my center post replaced on my A2 front sight. It was slightly bent. Cabelas replaced it and I took it to the range. Compared to the old center post it was installed lower and below the two "wings" of the sight. By the time I was actually hitting the bullseye at 25 yds the post was higher than the wings. Is that normal or should I have kept the post where it was and adjusted the height of the rear BUIS?
After that I mounted a new Truglo 48 x 2 red dot. I could not lower the dot enough to line up with the post when looking through the rear BUIS sight. I ran out of vertical adjustment. Do I need to buy a rail riser or should I bite the bullet and return the optic for a better sight? I was hoping to set it up for absolute co witness.

You have several issues going on here...

1. Co-witnessing that optic is probably not going to work. That optic has magnification (2x), making it more of a scope than a red dot. If it had no magnification, you could co-witness it and would need a riser.

2. What is your experience with the AR platform? Do you know how to properly use peep sights? Where is your eye in relation to the rear sight? What does your sight picture look like? You can not adjust the height of the Magpul BUIS that comes on the Sport II. Have someone else shoot your rifle and see if they get the same results to make sure it isn't you...

So if I want magnification (I was considering taking back the Truglo and buying a 1 to 4 power red dot) than my only option is to remove the scope if I need to use the BUIS?

In regard to the peep sight I only had to adjust the right left as it was very close in vertical adjustment. The rear sight has adjustment in both axes, the front post adjusts by screwing in and out the post. Should the center post be below the two wings?
This is my first AR, my other rifles are for deer hunting i.e. bolt actions.

Yes, you can not use the irons through an optic that has magnification. Even at 1x, because the glass is curved, not flat like a red dot, there is distortion. You could mount the scope on a quick release mount.

What rear sight do you have? The Magpul BUIS does not adjust vertically... it only adjusts for windage. Elevation must be adjusted with the front sight.

Your right. I stand corrected but had to take a look at it to verify. I guess I will settle for relying on the optics and go with the magnification. With just the BUIS, my eyesight is really not good enough to consistently hit the bull at 100 yds. This gun is really meant in my case for protection and also because I wanted to get it before November comes around. Thanks for your input.