I've been having more and more of a problem trying to get my AB800's to sync via the optical slave mode and would like to know if any others had some input for me.

I assume the optical sensor is on the back of the flash head, is this correct? I have done a few tests and this appears to be the case.

If so, does anyone know why? It would only make sense in a situation where you're using a light modifier like an umbrella, which I don't use much. I generally shoot bare or with a box of some sort.

That being said, what have you found to be the easiest way to sync via optical slave mode while outside, in an open field where the light isn't bouncing off everything?

I've gone as far as someone holding up one of the 7" reflectors directly behind the strobe, thus reflecting the light back at the optical sensor and that worked, but you need an extra pair of hands, and possibly a ladder depending on where your light is :-)

I could bite the bullet and get another PocketWizard, but I'd like to see what others think. Thank you.

When i first got my x1600, i tried to get it to fire using the optical sync and couldn't get it to work unless i pointed another flash directly at the rear of it, in really close proximity. I shot an event a few months ago where my battery died on my trigger and had to cable the pack system of 2 lights and hope that they triggered the optical sensor on the X1600, and it worked flawlessly from over 10ft. Even people's PnS flashes were firing it, and it wasn't even facing their direction. I don't know why it started off so strangely.

Outdoors I always use pocket wizards.
If I need more than the three that I own, I just rent a few more for the shoot.

Indoors it is not necessary as the light is bouncing pretty much everywhere anyway.

Well you're pretty much stuck if you want to trigger the AB outdoors via the slave sensor, I started like you with 1 wireless receiver connected to one of the flashes and the other to get triggered by the sensor, but even in my garden I had problems, so I ended up buying a second receiver so both of them would trigger that way... Outside you need an extra set of hands or wireless. Inside its pretty much covered, although it also depends how you position your flashes I got miss fires a couple of times in my small studio when I only had 1 receiver, turned out the setup didn't help to bounce back the light to the slave sensor.

In the past I've put a silver umbrella on the rear side to catch the light when working outside with pretty good results.