Question on 360 crank balance

brian6pac said
I had a 400 Chevy SB with a Scat 9000 crank Internal balanced on the front and external balanced on the rear. It made no sense to me why but that is the way it was.

They could get enough weight in the front counterweights but not on the rears. Somewhat common on 4.25 and longer stroke BBC chevy cranks.