I really like the RCBS competition seater with the side window. I enjoy seeing that bullet wiggle & align itself in the funnel as it drops down in line with the case mouth!
I wish RCBS made these for all their rifle calibers even for hunting calibers. I'd buy 'em. They could be an option in their die sets or they could sell separate. For average reloaders (like me) they could even eliminate the micrometer head to keep costs down.
As to the original question, you could try fitting/lapping/bedding the seater bullet cone in the RCBS die for a better fit to improve run-out. While it may go against your grain, try a Lee die ring with the rubber "O" ring on the RCBS seater die. Just a thought.