MIRR function help needed

[mayday1028]

I have a calculation using MIRR that I think is very simple. I have several cash inflows and outflows on a monthly basis and I'm calculating the MIRR. However, when I make the finance rate higher, my MIRR goes up. Why would this be? I would think that if this is the cost of capital, the higher the rate, the lower my return on investment (MIRR) would be. Am I confused about what MIRR is telling me? Any help would be appreciated!