Hollow Wooden Board Maker Template Width

Hi,

I’ve created a template with HWB template maker and am now tracing it with CAD. I have just noticed that the spine notch width is consistently slightly smaller than the rib notch width even though they are both set to 6mm. I was going to draw them both in CAD at 6mm width but just though I’d ask if anyone can think of a reason the template may be set up like this?

Thanks, Mike