I have an OWL mounted on a 15"rail with a16" barrel. Right now I have the light mounted flush with the end of the rail but I started playing around with a vfg and with where I like it mounted I have to have the light set back 2"from the end of the rail to reach the switch.

I get a shadow of the FH and the edge of the front folding sight but otherwise it's doesn't appear to mess with the output. Any good reasons not to leave it here? Only options to get it back towards the end of the rail is to either but a shorter rail, ditch the vfg, or buy a different light with a remote switch.

You should place it where it works for you then play around with it.

I have a similar setup on a couple guns, light placed behind the front of the handguard (Modlite PLHv2) Although these have more throw, there's a shadow but nothing crazy and works fine.

For Surefire lights I place further forward because they are more spill/flood and cast a much larger shadow.

I'm not familiar with the OWL so test it out.

If you run a suppressor, the shadow will be exaggerated of course, and there's no way to get rid of it unless you push the light past the suppressor... And good luck with that. You can minimize it with a T.Rex light bar for example, but it will always be there.

I mounted the Streamlight RM2 halfway down on the top of the rail. There's a small shadow in the lower 10% of the eye box but you don't really notice it especially at night at 50 yd or more.

If my optic was maybe .2" elevated I wouldn't even see that. My main goal was to avoid hanging the light off center line and too far at the end of the rail - personal preference.