[ILLusion]

I think the answer to "why" is pretty simple:

Close your weak eye and holding a pen with the tip pointing up, place the tip in the centre of your view, right in front of your eye. Let's say 1" away from your eye so that you don't poke your eye out.

Now move the pen to the side, let's say 5mm. Keeping your vision on something in the distance (the computer monitor you're reading this on, for example), note where the pen moved relative to your vision and the screen. For me, the pen started in the middle of the monitor, but after moving it only 5mm to the right, the pen was beyond the far right edge of my monitor. Move the pen tip back to the middle of your view so that it's back in the middle of the monitor again.

Now, while keeping the pen tip pointed upwards, extend your arm all the way out while keeping the pen tip in the middle of your field of view. Again, note where the pen tip is, relative to the monitor (we'll say the middle again) and move the pen tip to the side again, by the same amount you moved it before - 5mm. Note how little distance you've now covered? For me, I could barely get the tip past one word on my screen.




The other question that needs answering is "why don't all operators mount their RDS on the front of their outer barrel?" comes down to practicality and two main reasons IMHO:

1) Having the optics set further up on the end of the barrel makes the gun much more front-heavy, slowing down reaction time and initial shot readiness. Although having a heavy front-end gun makes the gun less susceptible to barrel climb, getting the front end steady for a shot can be an issue if the front is too heavy

2) Having the optics set further away from your eye reduces your field of view through the optics. Even with a tiny 20mm RDS, if it's set close to your eye, you can move your head around a significant distance and you'll still be able to view the dot inside the sight. However, if you set the optics at the very front of the gun, the slightest movement of your head can lose the dot, even with a massive 50mm red dot sight. Think back to my pen & monitor analogy.

In the end, it comes down to operator preference, finding that middle-ground between practicality, speed and accuracy.