Biggest thing is you're just going to have to learn whats best for you.
Different people have different flying-styles, and that affects when to chop throttle. Some will try and stay engaged in rolling scissors no matter what and are constantly working the throttle, others really don't like to do it for hell, and leave the throttle wide open and break off as soon as possible.
Personally, I cut throttle a bit or entirely whenever I went nose-low unless I was really trying to pack on the speed.
My advice, find someone to teach you the 109 in person, since that will be a lot more effective.