Studio lighting - firing a 3 head set-up

[Simpo Two]

I'm going to try a 3-head set-up for some portraiture.

I have three Elinchrom monobloc heads, and one can be triggered wirelessly by something similar to this:
https://www.amazon.co.uk/HWASTUDIO-channel-Wireles...

The other two have sensors so they can slave optically, but they're not in line of sight and I'm not convinced they're firing reliably. What I'd like is an optical sensor that can plug into the synch sockets and hang down so it can see the main head. I can't seem to find such a thing.

Would the cheapest fix be just to get two more of the widgets above?

[Turtle Shed]

The only time I've ever found this troublesome was when there was already a lot of ambient light (daylight in a marquee, so the flash heads were at full power and the light was bouncing off of nothing).

Otherwise, I've never had a problem. My flash heads (and they are fairly old and basic Lencarta ones) seem to fire pretty reliably when they sense a very quick change in light levels.

Of course the only true test here is to give it a go, because as you're well aware, you want it to work properly when you do the shoot.

[Simpo Two]

Thanks TS; I hadn't considered the ambient light issue. I'll do another test with the blind down and maybe some cardboard up for a semi-blackout.

[Simpo Two]

I found the problem - one of the buttons on the back controls the slave function! It just has an eye on it, very helpful...