It`seems to have been a two man job to set the fuze: IWM H 021133Presumably, the multi rails were all fuse set well prior to the engagement (proximity fuses in later models?) whereas the 2 rails had a body each to and could be fuse set and loaded in response to commands from the prediction set up.
I'm not aware of a radar type proximity fuze being used on UP rockets. There were attempts to make photocell type fuzes, but they never got past the trials stage. I think they were all time fuzed using El Cheapo burning fuzes. I would imagine the multi launch setups were all pre-fused to create a standard box barrage at various set heights, and you basically wait for a suitable bomber stream to fly at the selected height!
The radar type VT fuzes used on 3.7 and artillery natures needed to be spun to arm the fuze and energise the power pack. The 3" UP did not spin! (UP = "Unrotated Projectile")
I think it probably didn't matter in the case of V1s as they did't vary course either. If they travelled over AAA they didn't do anything to defeat the prediction so the guns or rockets could be layed on without any interruption.But were they set at significantly different altitudes to confuse defences?