Throughput

Hello Sir!
I have just watched your videos on Throughput and just come up with a doubt in the June 2011 paper Q5.
Part (b) asks for the optimum production plan, and the ranking according to the Return per factory hour is in the order B,C,A the marking scheme says the ranking should be done in the TA Ratio.
Although the ranking is the same if we use the TA Ratio or the Return per factor hour, it might not be the case in any other question. Just clarifying to know if we should in all cases just use the Return per factory hour to calculate our ranking.

Thank you!