Thanks for your suggestion. Well, it might be possible to control several options (like the Boundary Checking mode) of Spline Area(s) - for example by the Material ID of spline's segment separately and probably it's something feasible on open splines, but I'm not sure about the implementation on closed splines. We've added to our wish-list and we'll evaluate its possible implementation in future releases.
Something similar is actually possible by using multiple Spline Areas as different modes can be assigned to each of those. In attached sample scene, the Size Boundary Checking mode is selected for the closedSpline and the Edge Boundary Checking mode used for openSpline (sides).