I agree every hour over 40 to mean is more valuable to me so my 41st hour might be 1.1 times my standard rate, however my 60th hour might be 2 times my standard

I agree every hour over 40 to mean is more valuable to me so my 41st hour might be 1.1 times my standard rate, however my 60th hour might be 2 times my standard rate (the multipliers here mentioned are only for illustrative purposes). It would seem strange that a company would wish to purchase more hours at an increasing rate since the quality of the output from the later hours is likely diminishing.