I was shooting AR's with a friend of mine this weekend. He had an aquaintance build him an AR from mostly DPMS parts, including the two position Mangonel front BUIS. He was having issues getting things zeroed, so we took the time to measure all of his components against a couple of other stock guns.
In measuring everything, it looks like to co-witness, you would use the rear Mangonel notch, and set the rear sight and front sight blade accordingly. Our puzzlement has to do with the front Mangonel notch, which appears to be a bit higher than a standard FSB, and the fact that when the unit is deployed hastely, as it might need to be deployed, it automatically goes into the front and taller notch. Is there a reason for this? The only reason that I could pull out of my proverbial you know what is that perhaps you might want the point of impact to be closer to the bore at the close range where the sight might be deployed quickly, and without fumbling for the rear notch. Are we missing something here?