Indeed, a waste of time!
There is no registry entry involved when going from PgcEdit to ImgBurn, it's done via CLI.
As such, there would no way for ImgBurn to know where PgcEdit wanted the LB if you're rebooting and stuff.
After that, when burning in ImgBurn, a dialog box should pop up offering choices of where you can burn.
What info are you getting in that box?
Right click on the 'Sectors' value on the main screen and you'll can get an idea of where ImgBurn thinks a layer break can go - without needing to actually burn anything.