Daz,
Ive read with interest some of your posts regards WFP with 50L PF Trolley. Great piece of kit, i bought one a few months ago for some work i got thats not easily reached with the van system and other work too. Cant fault it. In my experience its safer to change barrels with around 5L left in them than running dry and getting an airlock. Then decant the excess to top up other barrels throughout the day so there is no waste and you use all the water you need for the job.
I noticed you asking about settings on the controller. I use 1mm pencil jets with 5mm pole hose and get the following results.
Setting 20 1.15 l/min
30 1.25 l/min
60 1.75 l/min
99 2.50 l/min
I generally wash on 20 covering all the windows and change to 60 for rinsing, i find this produces great results with a good curtain of water produced on the rinse, any more is overkill.
Hope this helps, good luck with the WFP its great once you master it.