does anyone know the focal length of a 8.5' solid Birdview dish. I did the cacalations of diameter and depth formula but it don't seem right the distance i come up with is 42 to 43 in. but when I measure from the scalar ring down to the center of the dish its only 39.25 in. what gives am i cacalating right or is the support legs to short they are the ones that came with the dish. i am measuring my depth from inside the dish do i need to measure depth on the outside of the dish. any response is very much appreicated.