Hi Rod,
Tacking a foil is about speed and precision and does not really require lift from the kite in order to complete a tack. However, having said this, the ability to learn to tack will be greatly improved by using a foil kite with a heap of lift. Shorter lines (15-17m) are also easier than longer lines (20-24m).
The trick is to be super fast and precise with your foot swap. If you have to look down at your feet, you haven't practiced enough. The footswap should be fast and an unconscious movement. You can practice this on the beach without the kite. Forget the back strap initially as back foot placement is not critical unless racing. The front gybe straps must be easy to get into and out of. Having deck grip under the straps can also slow the transition down whilst learning. The movement is a two step dance move. Back foot into front leeward strap as you go through the eye of the wind, immediately as you get your back foot into the other front strap (ie, you will have both feet in the two front straps), you remove your original front foot to the back foot position. The whole foot switch should take place in less than 2 seconds. Any longer and it is too late.
Speed and accuracy! This comes from muscle memory. Muscle memory comes from repetition, repetition comes from lots of practice on the beach before you get on the water. Until your foot switch is fast and unconscious, don't even bother trying to learn it on the water with the kite. The speed of your footswitch is racing the clock against the time you instigate the tack and begin an upward trajectory with the board and foil. The moment your back foot leaves the deck, the board will start to descend, until you get your previous front foot back on the tail to stop the dive back down off the foil. Foil kites give you extended time to get your balance, feet changed and tack the kite. Without the foil kite, you are relying on speed of foot change to happen before the dive back down of the board without kite lift.
Best to begin the footswitch from a low, close to the water foiling and pump the back foot to begin a high foot change before the descent. This will give you another second to complete the change. You can also benefit from a really floaty big front wing which will give you glide and time.
Once you get the footswitch fast and accurate, get a hold of a foil kite as the foil kite will give you the lift and time to make the footswitch whilst flying on the foil. Of course you can learn with a Peak4 or even an inflatable kite, but how far they sit back in the wind window makes it hard to duck the lines during the tack and also doesn't provide the lift.
Learning to tack a foil is the hardest thing to do on a foil which is why you see so many riding toeside and never changing feet. It takes a thousand attempts to nail your first one, and then thousands more to perfect it.
Baby steps
DM