I am using Commerce's commerce cart - see https://git.drupalcode.org/project/...

I am using Commerce's commerce cart - see https://git.drupalcode.org/project/dc_ajax_add_cart/blob/8.x-1.x/src/Ref... for the ajaxified cart. Therefore, I think that form display needs to be configured from the block. There is no need to change any code in the module.