I've got a 2.5-16 X 50 in an Armalite Ex0022 on my A4BF. The objective has about 1/4 inch clearance from the barrel.
If you look at the TBN pic on Armalite's site you'll see that the mount is forward on the rail. With mine in that position eye relief is correct, and the eye piece is about an inch in front of the charging handle. Cheek weld is good with the standard stock.
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