While I'm sure the pattern makes some difference in ultimate strength, I bet the total number of individual stitches has as much or more impact.

Also, our home machines can't handle the larger (higher strength) threads normally used on commercially produced straps. This makes me more comfortable using/recommending the "100%" pattern that has at least twice the stitches as the box pattern depicted.

I have used many different patterns for myself including multiple boxes. I've always used Gutermann's Mara 70 or Tera 40 threads. As long as there are a sufficient number of stitches to pass my "gut feeling" test, I'm happy and they never fail.

Disclaimer...I have a very well developed series of "gut feeling" tests that err on the side of safety.