bios – Restart Linux server on UPS after power restored

I have a Linux server on a UPS using network UPS tools (upsc). When there’s a power failure, after the battery runs low, it issues a shutdown command to the server, which is fine.
But when the power returns, the server doesn’t turn on. I do have auto-poweron after power failure enabled in the BIOS, and that works if I just yank the power. But doing a proper shutdown seems to prevent it from turning back on when the power is restored.

I know I could set up a RPi to send wake-on-lan packets every few minutes, but short of that is there anything I’m missing? What does a clean shutdown do to tell the BIOS not to auto-power-on?