Hi,
I had the same problem with the long adapter. I then tried the short one and it was only marginally better. I had to hog out a lot of material for a large job, I tried a number of cutters and lucked into a three flute .375 rougher which in my experience is far better for removing material fast, and not limited by the very short doc of the index cutter. The 17mm is retired after a short career.
Frank