Ok, I see now what you mean. I reread some stuff, and it is a little more clear. It should be tuned to maximum exciter power or 80 watts, whichever comes first. Then reduce drive to desired output. Am I correct yet?
You are getting close. It depends on what mode you will use. You would not want to load up to 80 watts (key down carrier) and then drop the power down to 50 watts and run CW. With CW your peak and average power is the same so the peak power will be 50 watts not 80 watts so you would be better off loading at 50 watts and not 80 watts. If you are running SSB and your peaks will be 80 watts and your average would be lower you would load at 80 watts regardless of what your average power might be because the amp must be loaded for the maximum peak so you do not get flat topping, splatter, etc. You would treat digital modes the same as CW. Whatever your radio can handle or whatever the amp can handle in that mode (whichever is the limiting factor) you will load at that level.