Thank you for the response and really good advice.
For HD setups I assumed the only place to mount red dots was behind the ejector port and was thinking nothing of it at the time. That makes total sense and feel that placement was determined by the guns design. It wasn't until I bought my 22lr pistol that I started to notice the longer rails for fore and aft movement.
Just going by feel before I hit the range, I tried three positions mounted on the rail. Forward, center and back. With all three locations I tested, by raising my arms from a gun pointed down position and see where the dot naturally landed. At the middle and forward locations I seemed to locate the dot faster, rear position I had to hunt for it. This is why I asked if there was a science behind mounting the RDS. Anyways, I appreciate the advice, thank you.