I think your system is very well setup. Pump heat is really negligible so it's ok to opt for the shortest pipe configuration. Using different size tubes is good in your case, as bigger is always better if you can comfortably use it. As you use the wider pipes in the return path, that's very good because the water flows slower and at very low restriction, just what's needed for pump intake.
GL suggestion could be good to keep pipes shorter, but having the res in a high spot makes very easy to fill the loop and take out bubbles. That's a matter of taste.
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