I just did the test on Open Beta, I don't have your issue.
Maybe you should test your HOTAS assignment ?
I did the test at all ranges, up and down.
If I bump to 320Nm, then press radar up button, nothing happens.
If I bump to 160Nm, then press radar up button, radar sets to 320Nm.
And yes, maximum radar range is 80Nm, no matter what the target size is.
This is because the radar is High PRF. Beyond 80Nm it wouldn't be able to telle the range.
Below 80Nm, it depends on target's radar cross section.