Okay, so my buddy mentioned that the forward mount has an adverse effect on the nice magwell center of gravity of the AR15. I tried some alternatives and found that this was true.
After about 20 minutes of exhaustive T&E, I concluded that the following was the best configuration for my needs. It strikes a good compromise b/w being forward enough, yet maintains the very good balance of the rifle.
[img]http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=15537[/img]
[img]http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=15538[/img]
You can see how this compares to a receiver mount with an #22M68 extension.
[img]http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=12878[/img]
You can see how this placement compares to a forward receiver mount with the straight riser. Admittedly, this receiver mount is probably one notch too far forward, but it never gave me any problems (note the short purchase of the forward half of the #22M68).
[img]http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=1811[/img]
HTH
PS Sorry my pics suck. They're down and dirty digital pics, taken with a digital videocam w/ a separate still photo chip (which is not of high quality). It's a great digital videocam, but only functions "okay" as a digital camera.