If you're really getting into the weeds on this, then lowering your seat 2.5mm would achieve the goal of keeping the same leg extension at the bottom of the crank rotation, but at the top you'd be a full 5mm shorter (2.5mm seat lower+2.5mm crank longer) at the top of the rotation. Since we're not professionals (most of us, anyway?) here, I'm not sure it's that big of a deal, but something to think about.