how to resize a shape without changing radius

I've drawn a shape I want to reuse for tabs and titlebars: a rectangle with the upper corners rounded and the lower corners square.

I duplicate this shape and want to reduce the width: so I select the shape, open the Transform dialogue, set the anchor point, make sure "Scale corners" is not selected, make sure "Constrain height and width" is not selected, and enter the required width at W.

Result? the "[do not]Scale corners" setting is ignored, and corner radius is reduced.

The only way I've found to resize without changing the corner radius is direct select, Transform, resize by hand, wait for Transform dialogue to display new width, rinse and repeat until I get the width I want.

Is there really no easier way?

Illustrator CC 19.2.19, in case I'm missing something.