But Harry could surf gently through Hermione's memories for now, ride on the back of the ones Ron's control spells were forcing to her surface to torture her. Eventually, Harry would redirect these to Percy, but he would have to get back into his own mind to do that. Right now, Harry trusted Hermione's subconscious mind would give him what he needed, would somehow recognise his presence and try to join with it to fight against Ron. It might even help him let her know he was there, without spooking her too much.