I don't see plug fowling being much of an issue with PFLs and think that the "walming to clear the plugs" is a hangover from WW2.
Only two things can fowl the plugs
1 The fuel, this can have an fowling effect from not burning hot enough but the odd PFL would not be enough to result in this........50 hours of flight trainning might.
2 Engine oil going past the rings!. if this is happening the cylinders need to come off. Both my C152's burn about 1 USQT between 50 hour oil changes so I think that in a well maintaned engine oil fowling is not an issue.
As I said i think plug fowling may well have been an issue with a Tiger Moth that was being thrashed in a WW2 training enviroment but not with a modern anerican engine.
I would take a guess that BFISK has has a bit of induction ice!