Issue using SetOptions to override default values of optional arguments

I’m running into a problem trying to use the SetOptions function to customise the default values of optional arguments for several built-in functions. The problem I’m experiencing is that overriding the default values of some optional arguments for some built-in functions does not appear to have the effect I’d expect, as illustrated by the attached notebook which focusses on the built-in Grid and Plot functions. I’m running Mathematica v12.2.0 on a Mac.

Any suggestions/advice to help resolve this issue would be much appreciated.

Thanks in anticipation,

Ian

SettingOptions.nb (55 KB)