Yup, the mustang doesn't have the strongest chassis, so it is normal for it to flex when jacking. The SN95 is still a huge improvement on the fox body. If I jack one of the back corners slightly, the hatch won't close.
As everyone else has stated, the best jack points are anywhere along your Maximum Motorsports XL Full-Length Subframe Connectors :SNSign: I still don't know why Ford thought it was a good idea to save the $30 by not installing some from the factory.