There are some great high intensity techniques you can use on medial delts that are safe and will lead to big time results.

For example, use heavy eccentric loads on a machine laterals. The proper way to do these is by doing the positive/concentric part of the exercise on your own, then have your training partner push down during the eccentric/negative part as you resist maximally.

I love these because unlike many negative protocols, they're safe to execute (most heavy negatives aren't), and they seem to really "dig down deep" into the medial delt muscle fibers.

Related:  The 12 Best Ways to Build Shoulders

Related:  Shoulder Training – The Mountain Dog Way