Anyone have a theory as to why the 606 might be more prone to ring sticking when running vegetable oil than say a 617 engine?

I've seen very few, if any references to stuck rings and/or very excessive blowby (pushing out dipsticks and/or blowing oil from the fill caps) on 617's but there are several instances reported here and elsewhere with the 606 engines.

There are clearly differences in the engines but I can't see anything that should make a 606 less tolerant than a 617. Any theories?