Any way to unlock advertised build area?

[yaqwsx]

There is no way to "unlock" the whole area without a hardware mode (a non-trivial one). See [1]. There is a flange in the base plate on top of which the display sits all over the display hole circumstance. This flange is 2.5mm wide and shadows a part of the display. You could mill away the flange on the longer sides and leave it only the shorter one. However, it requires some hard skills.

[1] https://photos.app.goo.gl/UcBRdh6bW1fHFfke8