Yeah, it's definitely possible that other issues are responsible here. I think scapular mobility and flexibility is fairly decent though. I will post some pictures later of posture.
The problem is that when I try to patch over the affected shoulder area, I get a different reaction than when I patch over the knee or elbow. In the case of the patellar region, it is pretty much impossible to miss hitting the patellar tendon, in fact, I hit different portions of the tendon so as not to "overwork" one spot too much. In the elbow, if I patched too close to the triceps, it would feel slightly painful and ineffective. If I patched directly onto a tendon, I might get a slight itching sensation, but no pain - basically I could very easily tell if I was patching over a tendon or not.
In the case of my shoulder, the pain is not very localized (anterior region, I am guessing bicipital tendon?)... so I am doing my best to get a fix on the area of pain, but I am pretty sure I am patching over muscle overlying the tendon, because it starts hurting pretty soon (1-2 hours) after I patch. It's hard to say how much exactly, but I am guessing just a minimal amount of NO is getting to the area.