This is like saying you can get a 10% improvement in battery life by changing where you position the RAM on your motherboard.
There is just no universe in which placing an oil filter in one location or another is going to make such a difference. You'd have to mount it completely outside the engine, say sitting as a cylinder on top of the hood, and even there you are not going to get a 2mpg improvement.
Sorry we're talking about a hypothetical car engine, and as an analogy to software development. I'm not an expert in designing car engines like you, but acting like this example being not fully realistic is some kind of "gotcha" for the point I'm making is really frustrating.
The point that I am making (obviously, I think) is that tradeoffs exist, even if you don't think the right decision was made, your full view into the trade space is likely incomplete, or prioritizes something different than the engineers.
Based on the replies, saying there's a hypothetical 2mpg improvement to be had was a mistake, everyone is latching on to that like there's some actual engine we're investigating.