This 1.56 factor is the product of two 1.25 multipliers:
A majority of the output disconnect switches in combiner boxes are rated for continuous duty. Therefore, the second 1.25x factor doesn’t apply, only the first 1.25 factor applies. Therefore you can base the combiner box size on 1.25x the maximum current, not 1.56x. This usually allows you to use a smaller disconnect switch, saving hundreds of dollars on each combiner box.
The same thing goes for unfused DC disconnect switches rated for continuous duty, such as those by Eaton. However, the fuse assemblies are not rated for continuous duty, so you must use the 1.56 factor on Eaton’s fused disconnect switches.
Be careful, even if you have a continuous duty combiner box sized at 1.25x, the wiring and upstream OCPD must still be sized for 1.56x. So it could be perfectly acceptable to have a 200A disconnect combiner box being protected by a 250A upstream fuse!