It was my experience that firing the bigger ones was just the opposite....you shoveled more in and they'd burn it, but on the smaller fireboxes, you had to feed them more carefully or you could choke 'em and get into trouble pretty quickly.
My experience was on D&RGW narrow gauge K37's , K36's, K28's. Never got to fire a K27, which is smaller yet. I made my student trips on K37's, but first pay trip was on a K36 (484). I had a "master" teach me how...Pete Degani..what he showed me kept me out of lots of trouble later on when I got on a K28 (the 470's). I never lost steam or water on one, but there were a few anxious moments while I learned the finer points. After that, I preferred the smaller ones. They were more fun than hard work, even on the SV branch, once you learned how.