RBSE960 running at half speed

Easy check of the backhaul is to hardwire in a pc/laptop to the satellite and speed test it. That way you know its only using the backhaul and not the wireless front haul for the test. But I'd agree with everyone else on this, the 2x concrete walls are causing your slow down. They're great at blocking wifi. 

But even if it is lower, 500mbps is still more than anything most users are going to be able to use. Streaming 4k only takes 25-50mbps. So unless you're moving massive data amounts, 500mbps is still plenty of speed