When you have a dish with multiple LNB's, the offset angles is built into the mount holding the secondary LNB's. If the mounting hardware is off just a bit, there may be no way to tune it properly. Dish had a problem like that when they first came out with multiple LNB mounts. Since there's a 10 degree spread between the two satellites, which will also require accurate adjustments with the skew and elevation of the sister LNB's, I'd recommend a two dish installation for the best reception.
That way both LNB's are looking directly at the satellite. Whenever possible, a single dish application always nets better signal levels unless you have a monster dish designed for stationary mounting of the dish using multiple LNB's. At best, Dish's multi-LNB dishes nets a marginal signal level that falls within their specifications. As I found out, there's always more signal to be gained by using a single dish on each of the two or three satellites. Remember, companies like Dish are out for more bang for their buck, which doesn't necessarily mean maximum efficiency.
Just something you may want to consider since dishes of the size you need are relatively inexpensive. I've found that the parabolic shape of the economy dishes used by the satellite providers are marginal as well. Good parabolic dishes cost more, and that's something everyone wants to avoid, but shouldn't. It's the heart of the system. There are websites available that will tell you the skew angle, elevation of the dish and the azimuth from your location to these satellites. All you need is the GPS data from your location and the satellite name or location and it will calculate it for you. Happy hunting.