I have a query about ITA Matrix switch parameters, hope this is the best place for it !

I have formulated my query as follows:

Cairo International, Egypt (CAI)

LHR MIA LAX / alliance oneworld; f ~bc=Y

HNL

LAX MIA LHR / alliance oneworld; f ~bc=Y

Business Class or higher

which returns a ton of flights, but the cheapest ones are all BA Y for the first and last sectors (LHR-CAI-LHR) even though I specified "~bc=Y"

Does negation not work for booking class ? Is my syntax wrong ? Is the code wrong ?

Answers on a postcard please