I said something about ground effect, maybe what I should have said we started accelerating as soon as wheels were off the ground.
That being said, there's normally some influence from the ground up to about quarter wing span which would be 8 to 10 feet which probably isnt far off.
I cant honestly say if it helped because I wasnt going to skull drag a plane that isnt ready to fly any higher than I needed. I only ever thought of it as a bit of a circus trick anyway, it was taught as a rough field takeoff.