your question above got me thinking about the natural behavior of saidin and the nature behavior of saidar. We've heard the many descriptions of how various channelers describe saidar to be a calm ocean or river that must be directed in a gentle fashion (i.e. riverbank guides the river) and we've heard just as many descriptions of saidin being a raging flood of power etc ... I'm thinking saidin is much more like trying to clamp a shield on an open fire hydrant while saidar is more like screwing a cap on a bottle. Again it plays into the inherent differences in the way the power works.

Basically saidar has mass and saidin has velocity ... which would explain why a mixed circle would create more force if utilized correctly.