All three solutions allow you to see two locations (110 and 119) for a wider range of channel choices and future growth.
So, Dish 500 is the name of the 20" Dish that can see both 110W and 119W, but Dish 500 is also a condition that can be satisfied by having two 18" dishes with one aimed at 119W and one aimed at 110W. Do I need Dish 500?