One delt exercise that isn't seen much in the gym that can really help out the medial head are 'Arnold' or 'Scott' presses. Larry Scott pretty much invented the movement, and Arnold popularized it. Scott had a naturally narrow clavicle structure, so he spent a lot of time experimenting & came up with the movement to give himself some really nice cannonball shoulders in the end.
You'll need to drop the weight compared to regular dumbell presses, if you're doing them in proper form...maybe only 50's instead of 70's. Once you work your way up to 70's with proper form, your medial head will have had little choice but to get bigger.