F/D is Focal length/Diameter
but your focal length measured from the bottom center of the dish to a point just inside the feed throat. (Not to the lnbf holder)
I calculate your Focal length to be 86.75mm. and the F/D at .36
Thanks for the calculation so I think my f/D is .38 because a lot of similar dishes of mine are that 0.38, maybe I'm wrong but I bet I didn't measured correctly and my f/D is .38 but still I think the Invacom is not good at that low f/D (correct me if I'm wrong)