The top of the plastic reservoir is not flat, it has an angle. If you point that little vent to the rear, it sits higher than if you point it to the front. So it’s a little less likely to seep fluid in that position.
It’s a minor difference, but having run them both ways it seems better with the vent to the rear. It’s also a really easy thing to do, so even if it only makes a small difference why not do it? Easy and free.
