According to the [url]www.trijicon.com[/url],
All 1.5x16 Compact Acogs have: 2.4" Eye Relief (TA26-2/4/5, TA26R-2/4/5, TA44-2/4/5, TA44R-2/4/5)
All 1.5x24 Compact Acogs have: 3.6" Eye Relief (TA24-2/4/6, TA24R-2/4/6, TA45-2/4/6, TA45R-2/4/6)
All 2x20 Compact Acogs have: 2.1" Eye Relief (TA40-2/4/6, TA40R-2/4/6, TA47-2/4/6, TA47R-2/4/6)
All 3x24 Compact Acogs have: 1.4" Eye Relief (TA39-2/4/6, TA39R-2/4/6, TA50-2/4/6)
All 3.5x35 Acogs have: 2.4" Eye Relief (TA11, TA11B/C/D/E/F, TA11F-A)
All 4x32 Acogs have: 1.5" Eye Relief (TA01, TA01B/C, TAo1NSN, TA31, TA31A, TA31F)
All 5.5x50 Acogs have: 2.18" Eye Relief (TA55, TA55A)
Please also read the sticky thread entitled "Best General Purpose optic". New-Arguy states there: [url]http://www.ar15.com/forums/topic.html?b=3&f=18&t=139306&page=2[/url] that the eye relief on his TA-31 may be longer than 1.5", and that Trijicon's eye relief rating may be quite generous on their optics.