Why didn't you just run the ro/di line and kent float valve directly to the sump and let it the float valve kick it off instead. That's what I'm doing to mine is straight to the sump to the level I want.

I don't trust electronic devices for cases like top offs, too many go bad and cause major problems. Here's a question for you.
How many times in the past year have you had even minor little power outages?
Now how many times in the past year has your toilet overflowed?