I do all the way back.
I have heard of custom shoes or drilling to get cleats in the middle of the sole too.

From the gist of the dozens (hundreds?) of fit articles and videos I have ingested, cleats towards the rear will have you using your larger glute and hamstring muscles more.
If your cleats have been back, maybe you have overused those muscles and underused quads, and moving fwd has you using quads now, resulting in (perhaps temporary) speed gains.

I would postulate that cleats back, seat back relative to BB would be better for long distance and cleats fwd seat fwd would be better for shorter higher speed rides. ymmv.