C-H, that is a great riddle/brainteaser. The “trick” is 3ø versus 1ø power must be compared at the same voltage.

1.5 amperes at 230V 1ø is 345VA, where
1 ampere at 200V 3ø is 346.4VA, BUT
1 ampere at 230V 3ø is 398.4VA.
Ratioing, 345/398.4 yields 0.866, exactly as expected.

Does that help?