I'll go back to what Brian Burke said earlier this week, that the hold up could be term. It was widely reported that the Blues offered Backes a 4 year deal similar to the Bruins offer in 2016, but would not budge on adding a 5th year. Backes was 32 at the time.
Fast forwarding to Pietrangelo's situation, he will be 30 when his next contract kicks in. The Blues held the line on their captain in 2016 and wouldn't sign a deal to pay him until he was 37. Boston did. If we extrapolate the ages, that would mean that a similar "line in the sand" would have the Blues refusing to come off of an extension longer than 6 years to take Petro to 36, and his agent is likely dug in that an 8 year max extension is the going rate for players of his caliber.
If I'm Petro, I don't agree to an extension in the $8.5M-$9M range unless I'm getting max term. If I'm Army, the only way I offer Petro significantly more than what Josi got is if I am getting a significant concession in term. One of the things you often hear quoted from agents and GMs is that the total amount of the contract is generally far more important in these negotiations than AAV, while "fan based" discussions of contracts tend to focus more on AAV than on total dollars. I don't know Petro (or any of the players in this scenario for that matter) but I wonder if it is important to him to make more in total dollars on this deal than 90 and 91 got ($60M total) or if he has a specific number in mind. A $60M deal over 6 years would put his cap hit at $10M, so if he wants to surpass that without maxing out his term he will need to be at $10M+ for his AAV. On the other hand, it would be easy to get him above that $60M threshold on a max term deal because there is no way I see him at less than $8M AAV which would put him at $64M for the life of the deal.
Sorry for the long post, but I find this side of sports to be fascinating, especially in a cap environment when you have to balance the distribution of available compensation. I wish we knew more about the inner workings of these negotiations, and more importantly where the sticking points lie, but I certainly understand why neither side wants to negotiate this deal in public. Hopefully, if any of the points above are correct, we find a way to meet in the middle and get Petro back in the fold under something like a 7 year, $63M ($9M AAV) deal.