Maintain the same depth as the plant was grown in it's container.

Do NOT use fertilized potting soil for ericacious plants (azalea) .
These soils are great for things like impatiens and fuscias but not so
good for trees and shrubs.
The first year I would not be inclined to feed anything.
You can make the planting area an inch or two lower than the
surrounding ground to capture water but inside this you maintain the
plant at the same depth it was when grown in the pot or at the nursery.