That won't happen under the new system. The new form (PR450) requires that the percentage premium over minimum be stated on the form. Congregations will be required to keep the minister's salary at whatever percentage above minimum the minister started at. In the old system that was a mistake on the part of the minister, who should have insisted that the percentage premium above minimum be appended as an additional term of the call.
I got stuck in that situation in my second pastoral charge. I negotiated a salary above minimum and then never, ever, got a raise in 8 years because the minimum never quite caught up to the dollar figure on my call form. I loved the charge, stayed longer than the average and understood that it was my mistake in negotiating. And fundamentally it's not about the salary. Having said that, quite frankly it wouldn't have hurt that charge (or yours) to have matched the cost of living increases the UCC decided on. I still look back with fond memories to those eight years, but I also reflect on the fact that they were quite satisfied watching my family fall behind and increasingly struggle as my salary didn't rise with inflation or cost of living.
Even though your former minister stayed several more years, it might still be interesting to know what she thinks of your charge at least in regards to that particular issue.