Just guessing here, but one reason I plant mixed plots is sometimes they will feed on one plant, sometimes another. Best guess is they prefer certain growth phases for certain plants.
I was taught in school that a large portion of a Deer brain is dedicated to their sense of smell. And detecting predators isn't the only reason. They need trace elements in there diet and follow their nose to them while foraging. The Deer may be telling you there is some sort of soil deficiency. Phosphate or Potash maybe.
I plant a lot of Rape, they really hammer the young plants after the first frost. And again the new leaves in the spring. They may graze the plot all year somewhat, but really don't get interested in the seeds much until it gets cold out and winter hits. What I'm getting at is they may not graze a plot the whole growing season, some phases are more interesting than other growth phases.
Instinct (and their nose) is telling them what to eat and a large part of it is what is in the soil.
A good Acorn year and my plots might be empty. I hunt in the Oaks.