I don't think height affects the rate of JS training.
Also I don't agree with this speed training analysis part, where it says JS for wingmen trains IS in about 7-8 weeks. I've trained it for 10 consequtive weeks last season but never got a pop in IS. If it really does train IS, it must be ridiculously slow (btw the player I was training JS for wingmen last season was 19 year old).