Our arena is vaguely egg shaped. It is 150’ down the long side, but about 62’ on one short side and 75’ on the other. Instead of making the whole thing narrow, we opted to make the best of the weirdness and give ourselves a little extra space. The only time I notice the slope is going downhill, into the shorter short side, in an unbalanced canter. Jumping downhill can be tricky too, but I like it for helping me require a balanced, organized ride. Sometimes my young horse protests, however…
https://www.instagram.com/p/BfEOhmegA9l/?taken-by=sharkeyfarm
But most of the time it rides very easily.
https://www.instagram.com/p/BZRE_iBATAu/?taken-by=sharkeyfarm
I usually set grids and lines going uphill and singles downhill but I think that is habit more than anything else.