@tookemtoni ,
Both 'Arrange' and 'Advanced Arrange (Ext. Preview)' currently rely on user input to select what objects are arranged within the specified envelope(s). It does not separate anything based on material and/or thickness. This may be considered for future enhancement.
Automatic material, thickness, quantity detection (and manual overrides) is already available in the Nesting & Fabrication Extension which provides the advanced control you are seeking, and more. With this, you can also pre-define the available materials and corresponding sheet stock sizes (via Process Material Library). For your given example, it would create a Nest Study with 2 separate Nests - one for each unique material+thickness.
Regards,
Ravi J
Ravi Javia
Product Manager