Bootstrap-ui 3.0 horizontal forms

I’m using Bootstrap-UI ( version 3.0, so using Bootstrap 4.6.

I’m trying to create a form that has controls that are aligned horizontally with their labels using the instructions here -

This works fine except I can’t see how to define the default column distribution ie so that the classes for the label and the control container are something like col-4 and col-8 without any breakpoint defined.

If I try something like -

                  'align' => [
                    'left' => 4,
                    'middle' => 8,

The classes created are col-md-4 and col-md-8 ie it seems to default to md as the breakpoint for the columns.

I know this is a bit obscure but does anyone have any idea how to do what I want?