We've been using a logarithm curve since before you started posting so I assumed you had at least bothered to skim through the whole thread before posting. Removed the chart to avoid further confusion.

The derivative of number of coins would increase as the difficulty increased.

if you're using log

_{2}(x) as the number of coins per block and the number of blocks per time unit should be constant, then the formula for the number of coins per time unit as a function of difficulty would be

y' = log

_{2}(x)

The anti-derivative of that would be

x*(ln(x)-1))

-------------

ln(2)

Conclusion:

The number of coins per time unit wold be growing.