The ratio of carbonate vs bicarbonate changes with pH. Not only do corals build skeletons at different rates during day and night, but in a closed system of an aquarium, the ratio or carbonate vs bicarbonate changes during the day vs night due to pH changes that occur.
Also, as corals grow, they use exponentially more and more nutrients to continue building.
I think there are way to many variables to be truly linear.
Google calcium bicarbonate vs carbonate pH and you can see the relationship.
When I studied corals in college (it has been a few years) it wasn't really know whether corals preferred bicarb or carbonate. It wasn't clearly understood whether they took carbonate up directly or took up bicarb and used a proton pump to spit out protons to make carbonate themselves.
All in all stability is key. The three are all interrelated. Fluctuation in one level effects all three. Smaller changes are better than big changes. People often shoot for a goal of maintaining say 9 or 10DKH but don't monitor pH, which is critical.