Reference arm, mounting schematic:


The position/orientation of the M4-mounting holes(filled in blue) can be altered to any orientation other than a 12 o‘clock - 6 o‘clock position(as long as the distance between the two screws is maintained and the center point between them stays at the specified spindle to center-of-arm base distance). But, as you change the orientation of the screw holes, the overhang locking screw on the arm’s base will no longer be pointing to 3 o‘clock(easiest access), possibly resulting in a less convenient access to that screw.
The 222mm distance is a nominal value and depends on the distance between cartridge mounting holes and stylus tip(should be 9,5mm, but varies between manufacturers and carts).
The 226/8 mm distance is a guideline only. Different turntable dimensions require different positions of the tonearm in relation to the plinth. The given distance should leave ample room between the arm and the rim of the platter when the armwand is in it’s resting position(all the way to the right).
With non-standard platters like the Scheu/Eurolab platter(dia.320mm) it might be necessary to add another 2-3mm to the given distance(here: 226 + 3 = 229mm).
Addendum: The angle between the green line and the black horizontal line ought to be no
larger than 20°, 18-19° works well on most turntables.