Finding the right electrical junction box size
The fetched Omni junction box sizing page follows NEC 2020 Article 314.28. It distinguishes between straight pulls and angle or U-pulls because each case controls the minimum box dimension differently.
How to size junction boxes
Straight pull dimension >= 8 x largest conduit on that path
Angle or U-pull dimension >= 6 x largest conduit + sum of the other conduits on that row
Omni then takes the larger requirement for each box direction. This rebuild does the same by comparing the horizontal and vertical straight-pull dimensions against the angle-pull dimensions for the corresponding sides.
Source example
The default values reproduce the fetched worked example: a 2.5-inch horizontal straight pull, a left-side angle-pull row of 4, 1.5, 1.5, and 1 inch conduits, and a bottom row of three 2-inch conduits. That yields a recommended minimum box size of 28 x 16 inches.