Today as others have suggested I gave foiling behind a tinny with 5hp.
No way could I get up on the board from water start.
So I tried kneeling on my foilboard -still no go.
So what went wrong?
Gear was Slingshot school 24in mast with me now at session 7 with kite going ok mostly up on foil in sub 10kn. My specs 76kg long term strapless surfboard kite surfer and 70 yrs still loving new fun.

I'd say it's a combo of the pull of the boat coming from lower down and the fact that you're not in control of the power delivery as you are when diving your kite. It's probably just throwing you out a bit.

5hp on a tinny?
does it plane by itself with 2 people on board?

A 6hp might have been better, in my experience 4 or 5hp puts out half the power.. also did you try lying down to start with board facing same way as boat?

Yes I even got up on my knees and pumped over the wake which did lift briefly. Maybe motor a bit old or should not have had an observer in boat.
Tomorrow will be trying behind a cat type day boat with 65hp