You might ask over on the Tenn state forum. Several members over there are planer board guru's and should be able to tell you how to calculate the depth of your jig.
I "can" tell you that the jig is NOT going to be 6ft deep, with 6ft of line out from the planer board & running 0.8mph. It's likely to only be 3-4ft deep.
When "trolling" (any method) and your lines are at a 45deg angle in the water, you can tell about how deep your bait is by using the length of line out (below the water) multiplied by 0.6 -- and that will give you the running depth of the bait. So, like if you have 20ft of line out (below the surface) and it's angled at 45deg, then your bait is approx. 12ft deep. (20x0.6=12) And that's regardless of speed, so long as the line is at a 45deg angle. More or less speed can change the angle of the line, depending on how much weight is on the end of your line. A faster speed with a lighter bait & the angle is not going to be 45deg ... same as with slower speed & heavier bait. The math only works for the line being at a 45deg angle.