Ugh...I can't believe you're still fighting with this!
If it was my tank I would manually bump the calcium to about 400 (380 is fine), then in an hour bump the alkalinity up to 7 dKH (ish). Then increase the dosers by a couple mL. In 3 days repeat until you test one day and the numbers are still at 400 and 7, then you have the dosing amount right. Have you tried this sort of thing?
Once you have figured out the dosing amount you can manually bump up the levels to where you want them (say 420 and 8? whatever you want). You may need to manually bump up the levels once a week or so for the first month or two while the tank settles in. Plus, as the tank grows the demand will go up and you will have to bump the levels and the dosers. I was bumping my dosers up by 1-2 mL 2-3 times a month for a year, now I'm only increasing the dosers once a month or so.