The POSP 4x24 does allow you to use the iron sights under the scope. However, the scope blocks a lot of your field of view, so it's not as big an advantage as you might think.
I had a 4x24 on my SAR-1, but eventually decided an unmagnified Kobra collimator sight (same idea as an Eotech, though based on different optical principles) was a better fit to my needs. I wanted an optic that I could use for heads-up, both-eyes-open shooting at close ranges, that would still give me an accuracy improvement over the iron sights out to 300 yards or so, and the Kobra delivers that in spades:
And yes, Tantal is The Man when it comes to Kobras and other eastern bloc optics.
With the Kobra, you can see the front sight through the optic, but it sits too high to cowitness the irons; if it goes down, you can still shoot with the front sight only at CLOSE range, but it would be more practical to just yank the sight and shoot with the unobstructed irons.
You want the scope as close to the bore as possible for accuracy concerns........chris3
Actually, for a cartridge with a trajectory like a rainbow like the 7.62x39mm, having a tall sight height does have some advantages. What you lose in ultra-precise shot placement at very close ranges, you gain in maximum point-blank range for any given vital zone size.
With a Kobra (3.8 inch sight height to the center of the lens) and a 50-yard close zero, you are 2 inches high at 100, a max of 2.2 inches high at 125, 0.9 inch low at 200, and a 5-inch MPBR of around 220 yards. Using the dot-chevron reticle, you can use the chevron in close and the dot past 25 yards or so. With a lower sight height, you either have to go higher above the line of sight to get a decent MPBR, or settle for more holdover at moderate ranges, unless you go with a reticle with multiple aiming points like a POSP.