alternating tread stair design

[bigbirdtomah]

I'm going to use the basic design as drawn by John Raabe to use in our hunting cabin.  I see the tread is 11 1/4 inches wide.  I'm wondering how wide the cutout portion is?

[TheWire]

http://www.countryplans.com/alt_stair/

It looks like the cut out portion should over lap the toe kick underneath it by 1.5"  So it would depend on rise vs run.