When bin contents are created all bin contents are being set to fixed. Of course it should be set for the default bin but the customer should have an option to set it for other bins via a setting. Many/most times outside the default bin customers do not want the temporary overflow stock storage to be fixed. If they do have designated overflow bins per item they should be able to manually set them or asked when the contents is created if it should be set to fixed. This would remove much of the noise form the bin contents view fro bins without inventory.
There could be a setting on the location page to auto set bins to fixed (could be boolean or Yes/No/Ask).
Default bin is of course set to fixed.
Users could manually set overflow bins to fixed
if the new setting is set to False (do not auto create fixed bins) then other than the default bin for an item, when an item is placed in a bin it would not be marked as fixed in the bin contents.