You must both be right; your explantions seem highly plausible. It must be correct that advantage depends on ratio of (rope length pulled):(distance moving of boom).
My simple living-room experiment must be inaccuarate. And the general rule that only blocks on the object moved contribute to advantage, must be incorrect.

Thank you!

Stein

PS: I stick with my 10:1 setup for my Taipan 5.7, though.