By Ladyessex1
Leigh-on-Sea Essex,
United Kingdom 
Hello. My Sun King is flowering its head off & also flowered through the winter months too, it's a beauty.
It has got a bit big and was wondering if I could prune it back a bit, I know they don't need to be pruned but some of the branches are getting in the way.
Jackie xx
11 Apr, 2016
It maybe that you've planted it somewhere there isn't sufficient space for it - it wants to get up to 2.5 high and wide. And you're right, this plant is listed as prune group 1 - link to the RHS page giving details of that type of pruning below
https://www.rhs.org.uk/advice/profile?pid=549
11 Apr, 2016