Andy,
Thats a great result.
" The question that comes to mind for me, is that, how does the engine know how much oil to burn and how much to retain as a lubricant? "
My take on this is simply , the oil that comes into contact with the internals ,ie cylinder walls, piston crown, cylinder head are taken out of the combustion cycle. this could be due to vegitable oils unique dipolar molecule that bonds to metals, it is this bonding that makes them great lubricants too.
Stewart