I don't quite follow.A bishop on f4 can swap a knight on f6?You play both colors?
I don't know the london but if you give a position I'll give you an opinion.For better or worse 🙂
I have been playing the London System(1 d4 2 Nf3 3 Bf4) for over twenty years. In many variations, White will play h3 in order to avoid having his bishop exchanged for a knight after ...Nh5.