Rhododendron straggly

I have this bush , but it seems straggly and no real heart to the plant . New growth seems ok, and I do feed it with specialised food and only rain water. It’s bedded in the correct medium for plant growth . Can these bushes be cut back to promote growth or ? Any guidance appreciated .

 

Yes one of mine was given a severe haircut by the nursery, before I bought it and they kept it in a shady spot until it started to reshoot.