Digitizing for heavy cotton thread

[Schuey]

I was wondering if anyone had any tips for punching designs using a heavier cotton thread. I've had good results using it as a tackdown stitch for appliques(running and zigzags) but we've had issues trying to sew satin stitch text. The issue is birdnesting at the backing. The machine has been slowed to 400spm and both the top and bobbin thread's tension have been loosened as well. I've also decreased the densities of course. The letters are about 12-15mm high. I was wondering if there might be a different type of bobbin thread we should be using also. Thanks.

[digitizing.com]