How does research rate work?

Playing as Cathay, the game says I have 167% research rate. But tier I research still take 3 turn, tier II - 4 turns, and tier III is now 4 turns.

That seems off to me. 2 turns x 167% = 3.34 research. 3 turns x 167% = 5.01 research.

Is it bugged? Is there something I'm not understanding?