Where to begin? Start wtih the End Grain part!
Here's the first detail - the post to rails mortises - at full scale.
Look at either "2x4 Rail". Rather than a single mortise in the center of the 2x4, there will be TWO 10mm mortises. Ideally, you'd like the distance from outside face to the nearest mortise face, and the distance between the "inside" mortise faces to be equal. But to figure that out you need the thickness of your loose tenon, and thus the size of the mortises. Since the mortises will be done with the DOMINO, and it's METRIC, let's switch to metric. The 2x4's 1 1/2" thickness is real close to 38mm (38.1mm to be more precise).
So I've got 38mm of space to play with - and 20mm of that will be mortises. That leaves 18mm to be divyed up into three equal parts - or 6mm each. That means that the distance from reference face to the first mortise's centerline is 11mm ( 6mm plus half the tenon's 10mm thickness). So "A" =11mm Handy because there's a Fence to Mortise Centerline "preset" for 11mm (the 22mm "step" for centering a mortise on 22mm thick stock).
I want the set back / reveal for the face of the post to the outside face of the rail to be a minimum of 4mm in order to get the rail to interesect the post BEHIND the posts 1/8th inch quarter rounded corners. So "B" = 4mm.
Now that "A" and "B" are known, "C" must equal "A" plus "B" or 11mm plus 4mm. So "C" = 15mm.
It just so happens that the second mortise on the end grain mortised rail happened to work out to a Post Face to Mortise Centerline distance of 30mm. THAT happens to be the MAXIMUM Fence to Mortise Centerline distance the DOMINO can do (without a minor modification - more on that later).
Working backwards to get the fence settings for the second mortises - if you start with the Post Fence to Mortise Centerline of 30mm, you can calculate the Rail Fence to Mortise Centerline distance which is 30mm minus 4mm or 26mm.
Tired of all that "math"? Here's the results - illustrated even.
Note: The DOMINO has retractable "stop pins" whose inside distance to the mortise centerline is EXCALTY 37mm - why - I have no phreakin' idea but 37mm comes to 1.457" - not 1.5" or 1.375" - but 1.457". European machines - they're definitely different!
Kind of handy working with millimeters instead of fractional inches. With 25.4 mm per inch, 1 mm (0.039") is a bit over 1/32nd of an inch ( 0.0313")