At 6' I'm not sure I'd categorize it as dwarf....

As they reach maturity, rhododendrons produce more terminal flower buds and less terminal leaf buds. Happily yours was well planned to be perfect height for its site with no pruning and can be allowed to expend its energy in blooming.

Morz8 is right, 6' is considered tall for rhododendrons. Dwarf is 18". Technically they don't stop growing, but their growth rate gets very small.

[Some plants that are planted in areas that they don't like will get smaller each year. An example of that is the Rhododendron Purple Splendor in Pennsylvania.]

Don't ignore your plant. In another 10 years it could get several inches taller. One way to make sure it stays nice is to take cut flowers each spring from the tallest flowers. If you ever had to prune it, always prune right after it blooms, because shortly after that it starts producing the flower buds for the following year.