Mahonia branches

Hello friends.
We love our 2ft tall mahonia plants (winter sun & lionel fortescue), they are happy & growing very well. We would like them to branch out sideways and fill more space instead of growing straight up. When & where should we prune them to acheive this?

 

You could take the tip out in April to encourage new branches to form. Well April is the correct month for pruning Mahonia, personally I would take it out now.

 

Many thanks Palustris. Will try that. Steve.