Can anyone make a recommendation for a rear BUIS that has a larger than normal aperture? I'm a little worried that even with the extended rail, the rear sight may still be mounted too forward to use even the large AR-15/M4 aperture. Cameron? Anyone? The D&L Sports rear CQB Iron Sight looks promising, but it cost twice as much as the Chaos Extended Rail! http://www.dlsports.com/cqb.html