Oh man, this is a tough one. You've done a lot already and the Cellspot is normally the best fix for signal in a specific area other than Wi-Fi. Since the coverage is fair where you are, the best bet is to file a Service Complaint with our Tech Care folks. I know engineering is aware of where we can use some coverage "love" but a Service Complaint's a great way to have this reported.
Just want to make sure we get you some help with this. Please reply and let us know if you still need assistance.
Checking in here one last time to see how things are going. Please let us know if you still need help.