It appears to me that the finished width of the diagonal strips should be about 1.4 times (square root of 2, to be exact) the width of the rectangle side strips.
Example:
The side strips "finish" at 1 inch - the strips are cut 1-1/2 inches wide
The diagonal strips "finish" at 1.4 inch - (which is very close to 3/8 inch) - cut a "generous" 1-5/8 inch strip
The side strips "finish" at 1-1/2 inches - the strips are cut 2 inches wide
The diagonal strips "finish" at 1.4 x 1.5 = 2.1 inches (very close to 2-1/8 inches) - cut a "scant" 2-5/8 inch strip.
Generous - a couple of threads "over" - scant - a couple of threads "less"