RE: Carve 122 or 133 ?? Final decision
Was your board "drifiting" downwind when you were fully planing, or
when you were slogging along SUB planing?
Sounds like you may have 2 issues to work on here.
First, if you really learn to put ALL of your weight on the harness, harness lines and the rig, the rig will support virtually all of your weight.
So, there's no more weight on your feet, and whether you are in the center rear foot strap or the outboard rear footstrap, there's virtually no weight on your feet.
Your upper body is pretty far (as long as your arms will reach) off the upwind side of the board, and your legs are nearly parallel with the surface of the water. In this position, it's pretty hard to put any real "weight" on your feet.
You use your legs, ankles, and feet to slightly "tip" your board so it goes upwind when you tip it slightly lee rail down, and it goes downwind when you tip it alot more lee rail down.
OR, if you aren't fully planing, you can tip the board a little bit upwind rail down to go upwind, but this is somewhat slower (due to the additional drag of having alot more of the board in contact with the water).
So, if you get into the outboard rear footstrap, pull UP slightly with your front foot, and concentrate on pushing "ACROSS the top of the fin" with your back foot, your board will tip slightly to leeward (you control the amount of "tip" (the roll axis trim) with your front foot and your rear ankle) so your board begins to go upwind on the lift created by the fin rather than the shape in the bottom of your board.
2nd issue is that you may be trying to get back into the footstraps a little too soon.
Try to make this a progression based on the acceleration (speed) of the board. As long as the board is gaining speed, you are moving back at the correct rate. If the nose pops up, or the board "sticks" at one speed, you've either moved back too far too fast (nose pops up here) or you are moving back too slowly and the nose is not coming up high enough for your board to slide easily on to a plane where it can accelerate even more.
Until the board is really moving well, and on a full plane, it's too early to put your back foot into the strap (centerline or outboard).
Perhaps, you've been moving back a little too quickly and not getting enough speed for the outboard back strap to work.
The centerline strap is more forgiving here as it's closer to the center of your board, and you can get into it a little earlier without upsetting the acceleration.
So, get your weight off the board and onto the rig BEFORE you even think about getting into the back strap (front strap is OK here as it gives you an "attachment point", but don't put any weight on that front foot).
Then when the board is fully planing, you are completely hooked in, and have virtually all your weight on the rig, then think about finding that outboard and back rear footstrap.
Hope this helps,