Do u also run a float valve or no. I have one installed, im debating on running the top sensor just below it or beside it.I have effectively the same mixing station setup. I have two apex optical sensors (with magnetic mounts) on each tank. I use them as safety overrides.
One near the bottom. Acts as a Fill Me Up sensor - and an override to forcibly turn off the heater in the tank. (each tank has it's own Apex temp sensor and heater - they're in my garage).
The other as high as I could place it. Acts as a Too-Full sensor - and an override to forcibly turn off either the RO Unit (on the RO tank) or the Fill Pump (on the salt tank)
BTW, these aren't perfect. I need to tooth brush them every time I do maintenance in the tank. And I really like them magnetic, so I can remove them easily when I take the tanks into the yard for the once a year thorough cleaning. I like to move them to the back deck. Temporarily plug output bulk head. Fill with garden hose, add a gallon of pool acid, wait an hour, dump/rinse/dump/rinse/dump/rinse. Removes all traces of salt/bio junk.