Spatial withinCircle distances

Hello,

I'm using Jena version 2.11.1. When I use withinCircle, I don't see results that I would expect - I am able to plot a set of points in a geospatial application and measure the distance from point 1 to the other points - they are all within 700 miles of point 1. When I do a similar query using the withinCircle API in spatial Jena, I don't get any points! When I double 700 mi to 1400 miles I get the results I expected with 700 miles.

Am I using the API incorrectly? Does the withinCircle use the number I pass in as a diameter of a circle centered at the POINT and not a radius from the POINT?

thanks,

-heidi