On my WinCE device I use Primo 9.6.13.405512 "Civic" which needs these 2 commands to make it sleep on power off and resume on power on, which is what I believe you want.

[interface]
shutdown_time=5 ;time in seconds for automatic sleep mode when power is disconnected. Can be any number between 1 and 9

[power]
skip_suspend_process_all=1

I hope this does what you want

Note: Some builds of Primo, e.g. Boki's "Kia", have these commands embedded in one of the .ini files so nothing is needed in sys.txt. This is why many users do not understand the problem.