Randy, I don’t know about the geometry/math of the cone angles, but from practical experience can tell you that with LS on forward view, you will see both straight under and a little behind the transducer if mounted 2′ down. The dead-zone I’m most familiar with is the 12″-16″off of true bottom. You won’t often see bottom hugging fish that are literally belly on the bottom, until they rise up a foot or so.
My experience is that LS isn’t great on forward view in water under, say, 6 feet. Perspective mode may be the answer though. Can’t say, I don’t use it in that mode since I run a HB360.
Before you dive in to the expensive world of FFS, just know that some folks, including me, believe that the powerful LS signal seems to turn-off alot of shallow fish when ice fishing – and even a fair amount of deep fish. From my experience, the range at which fish begin to sense and respond negatively to the LS signal is around 40′ from the transducer, so this is not as much of a problem in open water when making +100′ casts, if that’s how you fish.
On ice, I have had significantly better ice fishing success with my Vex and, when stubbornly sticking with the superior imagery of LS, will routinely get my butt handed to me by my fishing partners using a Vex or Humminbird, with all the other variables eliminated. Wanna clear a hole you just drilled over a big school of fish? Drop your LS in there and wait a minute or two. With a Vex or HB, you can sit over those fish and pound on them for a lot longer.
Just go into any purchase with your eyes wide open. LS does have a lot of pros, but fishing in shallow water on ice is not one of them IMO – from a catching perspective.
My $.02…