We have one in our garden that has been there for some years now, and they do make quite a big plant. I don't know, but perhaps it just needs more room at the roots. Ours flowers prolifically, and if it's very hot the flowers turn white, then get the red colour back when it cools down a bit. If you have a longish branch towards the ground they are very easy to propagate by scraping the bark from one side of the branch, then pinning it into the soil. Leave it there until the next year, tug very gently and you will more than likely find it has rooted and you can cut it free and plant another one out. I also wait until all risk of frost has passed and then trim the shrub quite hard, making sure that there are green shoots below where I cut it and it soon grows back again, flowering on growth made in the same season.
