Farda 1575 has a good signal here in MA many early evenings too, but Saudi 1521 has the edge, often by 10 dB or more.

UAE, being farther east, puts it in a better spot for bouncing in the "auroral doughnut hole" going your way as compared to more westerly Saudi Arabia that is likely hitting more of the highly-absorbing "doughnut" itself. Through-the-doughnut-hole propagation is why the Finns often have an easier time with DX from Seattle and Vancouver than from New York, Boston, and Montreal.

You are right in assessing the trajectory of Saudi 1521 towards east coast USA: over the Red Sea in a northwesterly direction for at least 100 km before running into the coast of Egypt. By that point the signal path is high enough off the ground that only a Himalayan-size mountain could have any effect. There are no mountains of that stature in that part of the world. Going towards the Pacific Northwest, the path - closer to true north - out of 1521 travels parallel to the shoreline and may indeed be over much more desert sand than salt water in that important initial 25 km run heading away from the towers. So between the auroral zone issues and the comparative outgoing "flight paths" of each station, it is not hard to see why 1575 would have the edge at your end while 1521 is more the "blaster" here.

Mark Connelly, WA1ION
Billerica, MA + South Yarmouth, MA, USA