Susanna Lewis' version of EZ Surprise Jacket

I'm working on a version of Elizabeth Zimmerman's Surprise jacket that was published with her permission in MacKnit Spring/Summer 1986.  The article was written by Susanna Lewis. There was an errata sheet for the instructions, which I have a copy of.   I plugged the instructions into an Excel Spreadsheet so that I can make multiple sizes and multiple gauges.

  This is how far I have gotten.

I'm doing it in approximately a size 24, using tuck stitch pattern 297 on KH-930 and two strands of 2-24 acrylic. 

My gauge swatch measures 15 rows per inch and 5.5 stitches per inch.  I think this means I need to decrease 1 stitch every 3 rows, approximately, to achieve a 45 degree angle, as a sense check.

Before I start the miter section that begins the sleeve back and front of the garment, I wanted to make absolutely sure of my math.

So using the instructions as given in the "recipe", I have calculated the magic formula to figure the decreases for a straight 45 degree angle.  Using that formula with my gauge, I am getting numbers that make no sense.

It tells me to decrease .73 stitches every 2 rows.   That is approximately 3/4 of a stitch.

I can't decrease .73 of a stitch.

I think I need to decrease 3 stitches every 8 rows, which I arrived at by multiplying by 4.  This is close to 1 stitch every 3 rows, but not quite.  I need to figure out the fudge factor.