boat speed = higher wake jumps?

I am a new guy and have been riding for a month. I was riding at 55' rope length at about 16.5mph and almost clearing both wakes (hs). Then we bumped the speed up to 17.5 and I was clearing it consistently (this may be cause the wake was closer together or was I getting more air...). So how does the boat speed relate to jump height and length?
Also should I be riding faster at longer rope lengths?
One last thing, on my toeside jump, my back foot keeps swinging around (like I am going to do a 180) and I can't figure out why? Thoughts?

Thanks for the help
Charles