Agree with Alex. Ditch the PP.
The one thing you need to do, is DECIDE YOUR CUES. You want him to back up with you raising your hands? Great, that's your "warning" cue. That's the cue that says to the horse, I'm going to ask you to back up in a minute. THEN, decide what you'll do if he doesn't do it right away. Wiggle the rope? Go to his head and put pressure on his halter? What works for YOU, is best. THEN, decide what you want to do if he STILL doesn't respond. It has to be a stronger aid, a tell rather than an ask. You can put MORE pressure on his head, wiggle the rope harder, whatever. There is no one "wrong aid". I know someone who uses the rope like a helicopter blade and just moves closer and closer and whirls it faster and faster, and if the horse doesn't move out of the way he eventually gets HARD whacks on the face.
MY backup aid is a hand on the chest, when I'm doing groundwork. Both my horses back beautifully from just that. The mare I'm working with at the moment likes to ignore. I go from THAT, to tap-tap-tap with my hand against their chest. And then depending on the horse, to SMACK-SMACK-SMACK on their chest, OR to BANG BANG BANG on the leadrope as head pressure. I escalate harder and harder from there until the horse goes backwards.
You need to establish personal space with this horse, if he swings his head into you as an evasion. You have a bubble around you that he is to stay OUT of at ALL times unless you invite him in, and you need to decide the uncomfortable thing you will do when he invades that space. I smack whatever part of the horse enters my space unbidden. You don't have to do THAT, but you do have to do SOMETHING, and be FIRM about it.
With the tapping, if he's ignoring your tapping, TAP HARDER. And harder, and harder, until he MOVES. And it has to be the PART of him you're tapping. My gelding has sticky hindquarters, so I work on him moving them NOW... I jump from a light tap to a HARD tap because my boy knows what I'm asking for and he needs to do it WHEN he is told, not in 5 minutes time when I've worked up to the strong demand.
Timing is key when you're using anything Parelli. If you stop tapping just a fraction of a second too early, or too late, you create problems... and not everybody has that kind of timing in them.
Ask, tell, demand, PROMISE. My perspective on that philosophy is to start with a very very small aid, like a whispered "please oh pretty please". If that's ignored, then you move up to a somewhat firmer aid - remember, clear boundaries between your phases of the aid - that's more along the lines of "ok move over" (using moving over as an example). From there, if that's ignored, "MOVE OVER NOW", and if you're STILL being ignored, "YOU WILL MOVE OVER RIGHT NOW OR YOU'LL WISH YOU WERE NEVER BORN"... the key to this method is to have a REALLY good "promise" phase, because that's your absolute last resort and you have nowhere to go from there. And it varies from horse to horse - a "promise" phase for your well-behaved pony might only be an "ask" phase for your rude gelding. It takes a very physically strong person to deal with some of these horses because people without a lot of physical strength may not be ABLE to have a really strong "promise" phase. Or, training aids! A whip, or spurs, can be incredibly effective with the horse that won't give you snappy transitions, or move sideways off your leg (or hand if you're doing groundwork)... I use spurs on my gelding when I'm doing dressage work because he otherwise refuses to move sideways off my leg. I used a bigger bit for a while when he wouldn't canter at jumps at a reasonable speed, because HE NEEDED A STRONGER PROMISE PHASE and my stick-arms with a very mild snaffle just weren't enough. He's back in a snaffle now and going beautifully, and he's getting softer to my leg on the flat.
Be firm. Be harsh if you must. But ALWAYS remember to give them the option of responding to a lighter ask, and then ALWAYS remember to have a REALLY good escalation if they ignore you. That's the only way to make them softer. And, like I said before, timing is key. If you stop the ask a split second too late, or too early, they just get worse.