The rule of sponging is.I have said it before on a few posts and that is that i have not seen with my own eyes a good finish achieved with a sponge...
1/ Only sponge 2 m2 at a time and trowel
2/ Use the sponge in a circular motion not straight lines like the clowns on you tube.
My method on board is. Fill out beads. Fill out tapered edges on boards. I have my finish on the stiff side. Give wall a coat of about 3mm of finish. Speedskim straight away. Let finish pick up a bit. Speedskim again! Takes seconds. Sponge and trowel straight away. Leave and then final trowel. Give one more quick flick across.
You cannot tell if the wall has been 1,2or3 coated and won't see a sponge mark.
Try it .