VPN disconnections are common while connected to a MiFi. VPN's by nature are picky on small drops that normally do not effect browsers or applications. This is designed to stop external threats from tampering with your connection but end up being a real pain in the field for daily use. I'd suggest looking into an Auto-Reconnect feature on your VPN's if you have one available to try and improve the user experience.
Try going through the usual reset steps (power cycle, pull the SIM, reset button under the back door) to see if the problem is temporary or not. If the problem persists try traveling to a different area to determine if it is location based or isolated to the MiFi hardware.
Comparing WiFi to the MiFi is not really apples to apples. The MiFi broadcasts its own WiFi signal as would any other wireless router. Chances are your disconnections are not in the WiFi area, but instead are related to your MiFi's connection to Verizon. I have seen many instances where a machine is freshly connected and starts to pull numerous updates that overwelm the connection and break the VPN tunnel. The only work around is to try and connect somewhere else temporarily until the updates are done and then migrate back to the MiFi.
Dormancy is not a feature that you can manipulate, it is a status indicator for your connection. All cellular devices go in and out of dormancy through out the day. As soon as your MiFi sends data across or recieves data from the network it will update its dormancy status accordingly.