As you know, I have a Reflex and an Aimpoint. My prefference between the two is actually Aimpoint, but I still love the Reflex.
I really, really think forward mounting dot sights offer A LOT of advantages over mounting them otherwise. It clears your field of view, allows quicker and better focus, aids in two eye open shooting and more.
Having said that, I think the best way to mount the Reflex is on a carry handle, not a flat top. There are not as many mounts for the Reflex as there is the Aimpoint, and none of them forward mount by themselves, except the carry handle mount.
You can get an ARMS 38ex, or GG&G FIRE Scout rail + the ARMS #15 Reflex mount. This will give you a little extention out over the handguards. But not nearly as much as a carry handle mount.
The ARMS #38S-ex will give you a rail all the way out to the front sight. That plus the ARMS #15 will get you as far out as you want to be. The ARMS SIR will, of course, do the same.
I have a lot of ARMS and GG&G gear. Which you should get largely depends on your overall package. For instance, if you were getting a flat top with M4 handguards, I would go GG&G FIRE rail, because only it fits over the fatter handguards (I really wish ARMS would do something about that). If you are talking about back up iron sights, I like the ARMS #40 over all the others. If you are talking Aimpoint mount direct to a flat top, I like the GG&G Cantilever as it offers good forward extention. If you are talking about an Aimpoint mount on a rail I like the ARMS unit because it is quick detatch. All of it is good gear, but some is better suited for specific set ups than others.