First of all the efficiency of the recipes is generally 10% and not 1 more item per level, which would be 100%, take in example the efficiency of furnaces, 10 of steel 5 of advanced circuit and 10 of stone bricks give me a furnace, if I want to give them 10% since before factorio 2. 0 there were no productivity methods with research I had to come up with a method, let's take level 1 efficiency of furnaces it requires me 100 of steel 50 of advanced circuit and 100 stone bricks, it obviously requires me 10 times the time of recipe vanilla, but it gives me in output 11 not 10 or 1, so if you go and do the calculations you get that vanilla gives me with 5 seconds of crafting so 0. 2 furnaces per second, with level 1 you get 0.216 furnaces per second, so even though it has numbers that seem totally off it is not, if you go and check the rates, which with factorio 2.0 tells you without the need for mods, you find that for the same amount of input items you have a small increase on the output given by the efficiency, and so on with all the recipes. I hope I explained myself at that how it works.