change morph drawable shape

[recoverrelax]

Hello. I have been trying this demo and i made a little adjustments, but i cant figure it out something.
I realised the morph Fab to Dialog shape is build depending of the dialog width/height ratio. for instance, if the dialog is a rectangle, the morphing fab will transform from a circle to a rectangle. but if the dialog is more like a square, the fab morphing will be from a circle to a circle. I want to achieve a 'rectangular' morph even with a square dialog shape. Can you give me a hint?