My bulb arc is almost exactly 220mm from my fres.

What is optimal??

I believe most people CLAIM to get best results a little more foward. Try moving it to 215/210mm.

This puts the theoretial point behind the arc slightly, meaning the arc tube is caught by the largest angle spread.

BTW, slightly foward worked best for me as well.

I'ld say turn on your pj and then slowly slide the bulb forward until you reach a max brightness. I found it to be about an extra 25mm forward. But yours may be slightly different.