if your rotating region is just barely past the tip of the blades, it sounds like you have not reviewed the recommendations for rotation regions. i would recommend starting there and also looking at the technical reference, solving engineering problems document, the help and the solidworks kb. rotating regions are difficult.
is i assume what you're working with. this looks like it may be outside the scope of what is recommended for rotating regions. you may want to check with your reseller on whether this is a good application for rotating regions. if a customer brought this type of project to me to solve from a consulting perspective, we would check with the developers first as the flow simulation rotating region method works for cases that are like pumps/impellers.