I'm rereading this section in BESM 4E (pages 259–260) and think it is pretty good advice for using Dynamic Powers, Power Flux, and Power Variation. I found the Dynamic Sorcery difficult to get my mind around in BESM 2E, and as far as I can tell there wasn't equivalent advice in BESM 3E, although I think its versions of Dynamic Powers, Power Flux, and Power Variation are very similiar to those in BESM 4E.
This section is also in Tri-Stat Core RPG (pages 157–158), as well.