Inside wall corners are rarely perfectly square. However, the installation tabs on the SHELF-E allow some flexibility in positioning the shelf. Therefore, you can move the shelf further into the corner when it is greater than 90° or further out when it is less than 90°. Keep in mind that you can consider the most common viewing angle of the shelf and square it to that wall surface, leaving the opposite wall a little further out. Ultimately, you’ll simply need to use your judgement to achieve an aesthetically pleasing application.