The caching parameters for GetStageBlend* apis are in the Finance Rules and Calculation Handbook on page 119, but in your case I don't think they're a problem - that cache is created by your call whichever way you want, worst that can happen is that you create an inefficient one, but numbers should still come through. (This said, I'd stick to one of the predefined shapes rather than going for Custom...)
I think the problem for you is more likely to be the Workflow Profile Name, which has to be complete - e.g. "SomeProfile.Import".
