I don't think the footstrap position has anything to do with jibing. When you step across the board with your downwind foot to transfer your weight to the rail for turning, where your other foot is located has little to do with the jibe, since 80% of your weight is on the foot out of the strap.
I can turn a formula board pretty quickly with both feet almost a meter apart on opposite rails. I can also increase the turning radius by how much weight transfers to the downwind foot.
As for flipping the sail, rounding up does indicate you may be flipping a little late. However, it may also be how you have the weight distributed on your feet. If you don't unweight the foot that was on the downwind rail at the right time, you will just keep carving regardless of what you do with the sail.
Also, if you lack speed, when you switch your feet 3/4 of the way through the jibe, you can sink the tail, which will round you up as well.
Bottom line, planing jibes take lots of practice. I have done 1000's and 1000's and still haven't perfected them.
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.