Last weekend I pushed my red sights to the end of my LR. (Aimpoint M4) I feel like my field of view improves as does my “both eyes open” while moving. Is there any downside moving my RDS forward as I have? 
I use mine right at the edge of the upper receiver. Works fine for me.
Forward on the receiver or on the rail all the way back against the receiver?
Still on the receiver:
It’s really a matter of preference, if you prefer it that far forward, than by all means leave it there, there is no right or wrong answer. A lot of guys use the LT cantilever mounts mounted all the way forward on the upper, putting the optic almost as far forward as you are describing. I have even seen pics with EOTechs mounted alll the way up by the FSB.
as mentioned above, I run mine all the way forward on the edge of the upper receiver, and pushed a little further via an ADM Cantilever.
I do it for the same reasons you alluded to - seems to open up my field of view a bit.
Downside - if you’re not semi-consistent with your position behind the optic, you may occasionally find yourself “hunting” for the dot. It’s not that big of a change, but noticeable versus an RDS with the eyepiece closer to your eye.
I put it at the front of the receiver as well. There are some people that advocate as far rear as possible. Their reasoning is that shooting a second target that is already in the FOV of the Aimpoint itself is faster. Personally, I can’t tell a difference.
*Note: There are some advocates that are very passionate about having the dot to the rear. I even read an article about a firearms instructor that regarded everybody that places the optic forward to be “newbies” and “know nothing about shooting.”
I prefer mine at the end of the receiver as well, in a LaRue cantilever mount. Main reason being it’s kind of impossible to slap a magnifier on if the RDS is mounted all the way back. 
[b]People are entitled to their own opinion.
It’s my opinion that none of these guys are “newbies” and they all know a lot about shooting.[/b] The location of each optic of these instructors is at the forward edge of the upper receiver.
With a rail that bridges the gap I put the sight as far forward as it will go with the lever still on the rail.
With a traditional setup with a delta ring I put the sight completely on the upper rec rail.
Buncha friggin noobs with their newfangled plasti-mags and red dots all forward and stuff…
Probably not even a accu-wedge in the whole group. Can’t imagine how they ever expect to be in “Tacti-Widget Monthly” with a Bush League effort like that…
I have a couple of Elbit Falcons and their original intended position is far forward over the handguard. It makes sense as it increases your “sight radius”, that being your eye and the red dot.
I like to get my RDS as close to the rear as possible while still allowing me to mount my 3X behind it. I think it is largely personal preference, but I have found that I am faster with it mounted closer to my eye. The mount and housing tend to blur out a little and all I’m left with is the dot. YMMV
Stephen
I seem to recall seeing that somewhere too. Want to remind me who the article was about?
When I started using an RDS about the time the ban ended I initially used a cantilever mount under my ML2 and put it on the far forward edge of the upper which put it out about as far forward as it could go. I used Compact ACOGs for awhile but when I went back to the Aimpoint I still stuck it on their in that type of mount and in that location.
Eventually I settled on mounting the 30mm Aimpoints in straight mounts at the same location because I found it balance better and gave me a better sight picture and allowed the tube to disappear the best with both eyes open.
When I went to the T-1, I instinctively pushed it all the way forward as well. I actually found that I started having problems finding the dot in unconventional positions. So I thought about it objectively and decided that instead of lining it up at the same forward position I’d line it up at the rear-most edge of where the 30mm Aimpoint lives. This worked out so well that I thought about it some more, and realized that the tube was a little smaller, moving it back even just one more notch would make it APPEAR to be about the same size as the 30mm tube, which would also mean that it would ghost out the same way. This is where the T-1 works best for me.
That rang a bell with me also, but for the life of me I can’t remember where I read it.
Here you go:
FIGHTING THROUGH THE RING
By Erik Lund, Senior Instructor
United States Shooting Academy
Yeah I don’t remember either, but Byron rescued us and provided us with the article.
Interesting enough I find the dot faster the further it is from my eye. Consistency is the key here.
My way is “A way, not the way” Eriks also is “A way, not the way”.