I have DD Omega X 12.0 FSP on my BCM 16" carbine. That's a 12" rail that looks pretty much the same as the rail in the pic bellow and I have it set up in a very similar manner with a streamlight TLR-1S mounted at 12 o'clock in front of the gas block and a tango down verticle grip under the gas block. I don't think I'd even seen this picture when I first set it up this way, but to me this is about as close to perfect as I can get with the placement of the light and verticle grip while retaining the original FSB.
I also have a BCM 16" mid-length with an Omega 9 rail that I also have set up with a TLR-1S, but I have to mount it at 3, 6, or 9 o'clock which means that the shadow of the barrel gets cast onto or at least close to my target in an awkward way. With the light mounted at 12 o'clock the barrel's shadow is cast bellow the target and pretty much out of view through my aimpoint, which is where I want the shadow to be. The only thing that would be a "more perfect" setup is if I could do the same thing to my mid-length without having to chop the FSB.
I prefer the mid-length gas system, but I like that I can mount my light at 12 o'clock with the Omega X 12 FSP, which requires a carbine length gas system. I like it so much that I am considering right now whether to just go ahead and chop the FSB on my mid-length and install a longer rail so that I can mount my light at 12 o'clock in the same manner. In fact, I think I may have just talked myself into it. :D
http://danieldefense.com/media/cta/AS1-vickers.jpg

