Quoted:
Now if you go to the full size ACOGs you have the 3.5X going back to a long eye relief and and then the 4X goes back short, I just dont see why a 1/2X difference can justfy going to such a short eye relief.

This RFI is to explore industry ability to correct the currently existing operational shortfall of combat optics. Current optics provide Close Quarters Battle (CQB) capability or the ability to improve target-hit probability at longer ranges, but not both. The ECOS will combine those capabilities in one optic. The SOPMOD Program is not seeking alternate sources for the current ACOG 4X (NSN 1240-01-412-6608) or ACOG Reflex sights (NSN 1240-01-435-1916), rather is interested in sources of COTS/NDI versatile, multi-function day optics with illuminated reticles for limited night use. It is desired that the ECOS also incorporate removable Anti-Reflection Devices (ARD) and threat Laser Protection Devices (LPD) to protect the shooter, and electro-optic systems from threat laser damage and laser optical detection. Two types or variants of the ECOS are sought. The first type, ECOS-C, is optimized for use on the M4 Carbine and provides a balance between CQB and mid-range aiming capability. ECOS-C will provide CQB capability, utilizing the illuminated reticle on unity or near-unity power (1x) as a reflex-type sight and will also provide magnification for enhanced target acquisition/identification. ECOS-C must attach to the M4A1 carbine MILSPEC 1913 Standard Rail. ECOS-C must have magnification capability from 1x at the lowest setting to 3-4x at the highest setting. ECOS-C must also have a capability to illuminate the reticle. This can be accomplished by battery power or other method, but must function in complete darkness as well as in bright light that may make low power illumination difficult for the operator to acquire. It is desired that a small dot in the center of the field of view is the only portion of the reticle illuminated. Vendors who have already fielded or are willing to produce an optic with similar capability should include that information in their response. The second variant of the ECOS that is sought will be optimized for long-range target engagement in conjunction with the Special Purpose Receiver (SPR). ECOS-SPR will provide limited CQB capability by utilizing the illuminated reticle on near-unity power (1x-2x) as a reflex-type sight, and will also provide increased magnification for enhanced target acquisition, identification, and engagement. The ECOS-SPR must also attach to the M4A1 carbine MILSPEC 1913 Standard Rail. ECOS-SPR must have magnification capability from 1x-2x at the lowest setting to 6-8x at the highest setting. ECOS-SPR must also have a capability to illuminate the reticle. This can be accomplished by battery power or other method, but must function in complete darkness as well as in bright light that may make low power illumination difficult for the operator to acquire. It is desired that the ECOS-SPR optic incorporate a ballistic cam setting indicator that the operator can view through the scope. Vendors who have already fielded or are willing to produce an optic with the ballistic cam indicator should include that information in their response.