IEEE 1584 Tables 2, 3, 4, and 6 have different factors for -
a) Low Voltage MCC & Panelboards, and
b) Low Voltage Switchgear.

For the same arcing current, a bus gap of 25mm for a) and 32mm for b) results in a significant difference in incident energy and arc flash boundary.

If the largest bus gap in Low Voltage MCC & Panelboards is 32mm, should it be classed as Low Voltage Switchgear ?

No. The "factor" is there to adjust for the general shape of the enclosures. Enclosure size and configuration makes a difference in incident energy. There will be a lot more detail of this nature in the next version of IEEE 1584. Do NOT make the mistake of assuming that the adjustment factor and the bus gap are tied directly to each other.

Also, as PaulEng knows and didn't elaborate on, the actual Arc Gap can vary from breaker to breaker, from gear to gear, and from bus bar configuration to configuration. Arcs are not always in a nice straight line. What you are doing with a study and the hazard analysis in 70E, is trying to determine what will happen in an accident and protect against the what could happen in an accident. This is not necessarily an easy or exact task.