yeah pushin them all the way back is deffinately the wrong thing to do cause ur just puttin full force onto their fingers and u wont be able to notice the very subtle difference...it literally is a very tiny difference in tnesion between the fingers u will hardly notice it sometimes
in all honesty its not my kind of thing i dont do the muscle reading or anythin like that.
my suggestion is to just re watch the video and go thru what matt tells u. tell them to focus on the one finger they are thinkin of, and then u need to push very lightly on their fingers one by one. the one that gives the most resistance is more than likely the one they are thinkin of. its not somethin u can practice on ur self u just have to go out and do it on someone.