I recently picked up a used, mint condition m600 ultra scout light. It came with the original box, diffuser, and the rm45 surefire offset mount. It doesn't have a tape switch or cap for a remote switch, only the standard tail cap switch.
This is my first dedicated long gun light, previously I had a tlr1 that was rotated between my handguns and long guns.

I need help with mounting position, I am having a hard time finding a good location that is comfortable to activate.

I currently just throw it on there with the standard mount at 3 o'clock, but I find it awkward to activate.
Should I go with the offset mount at 5 o'clock,
Or put it on the opposite side at 7 o'clock or even 9 o'clock with the standard mount, and keep my thumb forward instead of around the vertical grip?
I have the vertical grip in my regular spot but I am open to moving it around.

Here is a photo.

Is there a reason you don't want to get a tape switch? Having to fiddle with hand placement between manipulating the tailcap and shooting position will prove cumbersome, especially if you just need a splash of light. Otherwise, there is no magic light position. It's going to come down to what works best for your application and is comfortable.

I have four m600s and i have them offset between the 9 and 12 oclock positions. Easy and comfortable to hit the button.

I'm a righty and this is how I run mine. 

I'm not particularly against a remote switch, I was just wondering if my current set up would work before spending more money.
The remote switches are $150-160 from what I saw online. I would have to save up some before getting one.

I may go with the remote switch if I can't find a configuration I like with the tail cap switch.

Thanks Skylersa and JBecker_72.
I will try it on the opposite side both with and without the offset mount, at 9 and 11 o'clock positions.
I am running a single point sling so I don't have to worry about interference with the sling.

This set up also works well for me

A little update.

I moved it to the 11 o'clock position, it seems to be working out pretty well. I have to try it at the range in a couple of days.
I tried the regular mount first, it was OK but my thumb didn't line up as well as with the offset mount. Plus the offset is more streamlined.

I may want to go with a LaRue mount in the future, for the qd ability. If I did that I would wait till I saved up for the lower 1/3 mount and get them together.

Picture:

https://drive.google.com/file/d/0B3Z6oG2et7q-Q1BjeHlMMVJpQm8/view?usp=drivesdk

I do run pressure pads at the 12 o'clock and run the lights at 1.  I don't like the 9-11 light position as a righty and it banging my leg

I've got several Sf scout tail cap/remote switch sets that are brand new- I'll sell you one for $55.00 shipped

I was using an Arisaka momentary thumb-press/twist-for-constant model at 11 o'clock, but found that unless I had it backed out really far, the light would go on whenever the bolt slammed home.

I'm now using a Surefire SR07 at 11 o'clock with the light at 1 o'clock. I'm more or less using the the constant-on housing as a handstop for my thumb, and it's held in place with bands (I removed the rubber Picatinny bits to get it lower to the rail). Probably will lock it down with some good double-sided tape soon, but I haven't yet found something that's heat-resistant, thin, and not described as permanent.

I run mine forward in an offset mount. The bigger question is why run a vertical grip? I found it does not actually make me any faster than just holding forward and wrapping my thumb around the forend so long as I can run a slim enough rail to do so and have an adequately long rail. If you do run a VFG, never wrap your thumb around the grip, put the thumb high and pointed more forward on the off side, keep your index finger off the grip and forward of it on the rail. Your off hand for your carbine should resemble your pistol off hand.

Using the hand position that DevL describes, mount the light so that the clicky switch on the back of the light is near your left thumb (assuming you are right handed).  Don't place it so close that you could accidentally activate the light.

Tape switches don't work for me.  I want the force I apply to activate the light along the axis of the bore and as close to the bore as possible.  This minimizes moving off target during light activation.  A tape switch, unless mounted on the front or back of a vertical grip, places the force of light activation across the bore, which moves you off target.

Using a visible light laser mounted to your rifle and on a target, activate the light and see how much the laser moves off target.  Choose a position that minimizes the displacement.  If you don't have access to a laser, just place your RDS on target and activate.  The displacement will obviously be more apparent the greater the distance of the target.