It's cool, I doubt most people even realise their radiators have a coolant level
it only goes down when your radiators are over a 100% load after all.
As far as I've observed, the cells do not actually place or receive coolant to/from radiators, the rack just turns used coolant back into stored coolant and requires a connection to radiators for logical purposes.
The easiest way to observe this is placing a half-full coolant cell in- it won't charge back into full even if your radiators have coolant in them.