It takes out the slack, but the overall tension decreased just enough to slip slightly on the top end. I have seen it on a few dynos as well. I know Kenne Belle has a power steering spacer to take the tensioner back closer to max (similar to stock), but that sounds like much more work than just swapping out the idler if you have the supercharger off for a pulley change anyway. Originally my car had a jagged top end and the power flattened out. Went to a larger idler and power climbed and smoothed out considerably. Happened from about 5800rpms on.