I just happen to have one of the "Hornady New Dimension" universal seating dies in 20 caliber.
My preference in seating dies in the RCBS Competition die. The side window does it for me. Drop the bullet thru the side window and the guide sleeve keeps the bullet in place while it gets seated in the case neck.
With most of the others, you have to keep the bullet in place with your fingers as you raise the ram. More than once on the non Comp seaters, I've smashed my fingers on the up stroke.
The smaller the bullet, the harder it is to keep the bullet in place. Never have checked run out on the finished loaded round. Accuracy wise, never felt the need.