In the process evaluating my hand grip while doing thousands upon thousands of vertical, horizontal and curved stroke on practice paper I reached the conclusion I needed a custom fit pen holder. I began to mill my own double sided nib holders on a mini wood lathe as I needed a pen with a thick diameter similar to the Design markers I have used for over 3 decades. I have tried almost every commercially made pen holder and they have all felt odd in my hand grip. Many have been too small of a diameter to manipulate the nib.
I am just now having some success with dip nibs as the holders fit perfectly in my hand. They offer a shape to allow ease for pressurized strokes and control of stroke placement at any angle.