I don't think it would be the pressure so much as the heat transferred from the hot gas that might damage the radar antenna. 3 psi is actually a lot, but I doubt anything like that much was actually applied to that landing radar shield. It would have only had to block direct thermal radiation from the engine bell. I don't know how hot they get, but I've seen launch videos in which hypergolic second stage engines glow cherry red. They may or may not actually look like that to the naked eye -- CCD cameras are sensitive to the near IR -- but that's still a lot of heat if you're just a meter or so away.

Have you worked out the flow patterns of the DPS plume during landing? I'm curious to know just how the dust flowed, and why it didn't leave any appreciable amounts on the landing pads. The movies don't really give a sense of depth but it seems as though the plume went straight down and then out radially after hitting the surface, hugging it and taking dust with it. There would be nothing, no back pressure from an atmosphere, to launch the dust particles up at any angle from the surface.

Something else I've noticed in those movies: you see radial streaks in the dust sheet. I had always thought these were due to shadowing by rocks embedded in the surface, but they resemble the expanding, radial streaks of smoke I see looking down along launcher engine plumes in a vacuum. I don't know what they are, probably small eddies or instabilities in the plume as it leaves the engine bell.