just below 1.5l m2 opacity/coverage!
That is less than the manufacturer quotes! probably worth a call to them questioning opacity and hope they give you some, to finish the job at least.
In hindsight, perhaps it would have been better with a couple of initial coats of their normal masonary paint (watered down a touch) to get complete coverage and then 2 coats of the silicone paint, with a 5% watered down first coat.