It cost me 0.125 as well for a total of 0.356 drk to denominate a measly 17.999 DRK. Kind of expensive don't you think. And if denom is supposed to be .001 then why is it .0125 for some users? Another bug? Here's a screenshot. And no it's not photoshopped.
It is definitely charging .0125 per denomination round or .1 DRK for 8 rounds. Your math above seems off, but I agree that .0125 per round is too expensive, especially when anonymizing smaller amounts.
It was raised to 0.0125 per 1000 DRK per round from v30 because with 0.001 fees the transactions were not getting into blocks fast enough causing a lot of people to get stuck on 1 round.
Now it is fine for most people but there may be a problem with large amounts (camo).