All good Rick. The key dimensions of the drawing are attached.
Angle of the Y split from centre: determined from zooming in on the aperture mask in the PDF until it fit my whole monitor and calculated the rise/run, then arctan'd it, so 15.6 deg. Maybe I should have read up on the bahtinov first and stuck to 20 degrees, and assumed that the image in the PDF may have been squished.
Width of the obstruction: a value between FL/200 to FL/150 (though that should technically equal the bar+gap, not the bar? there's no equal gap here, so ....?) that fell onto a multiple of 0.4mm (the X/Y resolution the printer works well at), so 1.6mm. Maybe this should be halved.
Ok now that I think of it, a 20 deg angle (40 deg between bars) and 0.8mm obstruction might be the way to go if it doesn't work.
Well at least a photo of the first printed version of the mask wasn't posted here
