I think what you mean by this is "How does the Rebellion know that the shield is only around the Death Star II? And if they did believe this, why didn't they perform an orbital bombardment?""if I hear the hologram I want to hear how the Rebellion knows this said shield only protects the DS2 and not flash fry the genewrator from orbit"
If so, I can answer your question simply: they didn't believe that. What they did believe was that the shield protected the Death Star II and a small portion of the Endor atmosphere around the generator, possibly stretching all the way down to the surface of the planet. The reason why they didn't perform orbital bombardment is simple: the shield was protecting that small portion of Endor's atmosphere around the shield generator.
If your question is "How did they know this?" then my answer is: that was part of the information their bothan spies informed them of.
I agree that the shield generator projected a shield that protected both the Death Star II and Endor. The extent and scale of the shield's protection of Endor was limited, as shown by the hologram diagram.