Hi there - thanks for responding. 
I believe the "one light only if it's just two roads crossing" approach is consensus anyway, it's specifically the  ones on double carriageways that I'm concerned about. 

As far as redundancy is concerned, I'd argue it's the other way around - moving the lights into the center of the intersection, with no restrictions as to what specifically each of them applies to actually _introduces_ redundancy, bc now you have multiple "fake" (not applicable) lights no matter what direction you're moving. 
I understand the "I can't get it to work the other way" argument when mapping new/missing lights, I'd just ask to not move them if they're already mapped in the (more detailed) newer fashion. Does that sound acceptable?

If you care to find out how the approach arrows work, here's some details:
In the end, it's just another tag on the light itself: direction=forward (if the light applies to vehicles traveling in the same direction the way is drawn) or direction=backward (if the light applies to vehicles traveling the opposite direction).
If no direction tag is specified, the light applies to vehicles approaching from either direction.
However, if the light sits on a way that is tagged as oneway=yes (or oneway=1 I believe), you can omit the direction tags altogether (so on intersections where two dual carriageways cross, like IL59 / Royal Worlington Dr, you literally just place the light on the stop line on each of the incoming ways and that's it - no extra tags required).
The same approach works for stop signs too, by the way, not just lights.
