I know exactly what you are talking about. Seems to happen on my boat more with the starboard rudder. Letting out the main a tad and taking a step back towards the transom usually helps. However, it is slow. I have the rudders from #707.
IMO, I think the rudders on the Blade need to be redesigned. A friend has several extra 18ht rudders and I have really thought about trying those out on the Blade.