Troubleshooting pattern Brushes in AI

I'm familiar with pattern brushes in Ai but have not needed to make a new one for a long time.

This brush just does not want to behave. It's a simple concept- a hatching shading brush that replicsates the look of small drawing pen lines.

Problem is (see image) that it does not maintain the pattern's aspect ratio when used on the simple test path, which is just a basic path. The brush squashes the pattern to fit and changing the brush settings seems not to help.

The original I made the brush from is at bottom left in the screen grab.

Any ideas as to what I'm doing wrong? 🙂