Chunky fabric and welt pockets

I'm working on my first waistcoat and I am using a fabric that is thicker than your typical fabric. (I realized too late that this thicker fabric complicates everything, but I'm going to finish this sample before starting on another waistcoat with thinner, more "standard" suiting fabric! )

When following the steps for attaching and finishing the welt for the lower pocket, the multiple layers are making the corners of the welt very bulky. And turning under the top corner was very difficult.

Is there a different method to use on the inner fold back section of the welts when working with thicker fabrics?

Thanks!

Jenny