Perhaps Miss Lynn will help on this.
I wonder if the ratio of kidney to steak has a lot to do with the flavor?
It would affect it somewhat. I always use one third kidney, two thirds beef steak. The secret to taking away that bad liver/bitter/iron taste is covering your cubed kidneys with cold water and about a tablespoon of vinegar or lemon juice. Let them soak for at least an hour, two if you can. Drain and rinse in cold water. It really works to give them a delicate flavour.
Note: Be sure to remove the membrane from the center of the kidney and the fat before soaking, both contribute to peculiar taste.