Thanks for the BTN suggestion. I thought it would be super uncomfortable but I like it a lot. I haven't gone above 50lbs but I've just been doing high reps and my medial delts are already making some progress. The medial delts for me have always been super undeveloped so I am excited to see the changes so quickly. Thanks again.
BTN's are not recommended if you want to keep your neck and shoulders healthy and pain free.
O&G is correct as usual. Never do any resistance exercises behind the neck, push or pull. Read Bill DeSimone's works, they are very valuable here. Relevant links:
I have used these concepts for several years now, and have saved these aging joints much wear.