Interesting flow behavior on the Koolance. Perhaps there is some block expansion happening as flow and internal pressure increases causing that. I know I have seen some odd things in pressure drop curves flattening out like the GTX radiator series that was presumably due to the very thin tubes expanding under pressure.

Love the work and think the one mount concept first is very wise. Take care of that card and take your time. Enjoy the Vaca.. much deserved break!!