I found that I certainly could, with the small centreline tank, an R3R under each wing, 50% internal fuel, and full military power. When I stopped the test I was doing 550 km/h and increasing at 6 deg AoA in Recovery mode autopilot. I was using the default atmospheric settings in the mission editor.
Could you share your exact settings so I can try to recreate?
EDIT: Actually, looking at your post again ("weight around 20500 lbs"), you must be using full internal fuel? Using that weight I agree with your findings, but I dunno if that's what the table assumes.