The system is reactive not predictive, so it takes a few wipes before it can assess how heavily the rain is failing. Very fine rain can require a different setting to heavy 'summer' rain.
I found the system worked well on both my RCs and on my RX. Better than the system on the Mercs, where no adjustment was possible.
Also be aware it is possible to set the wipers to intermittent operation, check the handbook.
I think patience is sometimes required for the system to settle down