Demons concealing mana

It’s stated that demons don’t conceal their mana levels from one another as a status symbol, and from their enemies out of pride. But they’re consistently portrayed as cunning creatures who feel no obligation to the truth and no regard for even one another. Why would it not be more to their advantage to occasionally flash their true mana level when intimidating subordinates and otherwise keep it secret so that enemies or rival demons are more vulnerable to sudden stealth attacks? Even a demon with more mana than you can be eliminated by surprise if he doesn’t have any real idea what you’re capable of.