I can't really give you any advice on a ratio because I've never used that product line, but you basically want to swap some of the grow for bloom, while keeping ppm consistent. It's probably too late to do anything too drastic now anyway,and the plants aren't that bad so there's probably nothing wrong with just continuing on your current plan. Flushing time varies with medium, how big your plants are compared to their pots and how much water you put through them. I don't like the idea of 3-4 times the volume of the pot that just sounds like a waste of water so I just try to pick a time to taper off my feed then let the plants slowly consume what's left in the pots until harvest. At the end I'll run a bit more water through to make sure the last few days are spent in a really low ppm medium.