i too made a cut out but mine is a little different, its 30cm long, w/ a 90° included angle...then its marked again on one side, parallel to the edge at 20 and 17 cm. then i drew a slightly wider angle line at 110° for ortf. it was a big triangle but i cut off the bottom making it a trapezoid, about 3in tall. then i cut into the middle of the shorter part (the side that doesnt have angles marked) a 90° corner for XY or other 90° checking. basically, i can put it in between my mics (stacked vert bar style) and see if the mic is parallel with the line it should be, and if the cap is in the middle of the marking for distance. i hope that just made sense.
also, i have learned that w/ my homemade vert bar and SP c4s and SP shocks...NOS is mics in middle of shocks, shocks extended to full length, DIN is mics in middle, shocks bent to 90° angles. ORTF is the only one i really bust out the cardboard for.