Colin- print out the text about from the OW site about lounge access being that of the longhaul class when connecting to/from a lower class just in case the F lounge attendent challenges the rule. I had a BA LHR F attendent challenge my admission as AA EXP-OW emerald and she asked me if I had anything in print (like show your FF card with applicable OW gem code plus a copy of the rules that you are entitled to access as we don't know/won't admit to the rules) Much easier to present the rules than wait for the attendent to call a higher up who also might not know the rules.

Hope you get a chance to visit the lounge between flights!