I don’t know the answer. I own the same enlarger with the 670 MXL head. Per the KHB site, the “7700 MX” intended for the Canadian market is the same head as the 670 MXL head in the U.S. market. So, other than the markings, it’s the same thing.
The LPL Enlarger Guide_ KHB Photografix.pdf (ianbfoto.com)
The maximum density number of a system for variable-strength dichroic filtration is arbitrary. When the filter is fully retracted from the light path, the dial reads 0 for all scales. When the filter is fully into the light path, the dial reads whatever maximum numerical value the scale provides.
Depending on the maker’s practice, the maximum numerical values for a dichroic filter can be 130, 170, 200, or whatever numerical value the maker chose. I think (but am not certain) that these all describe the
same maximum filtration.
We can speculate about the reasons for the lower maximum filter value for the magenta filter compared to the higher values for cyan and yellow on the LPL head. But that’s only guessing.
Here’s my guess. The magenta filter used on the LPL head has a maximum effect that is
relatively less than that of the cyan and yellow filters. Therefore, relative to the cyan and yellow filters, when the magenta filter is fully into the light path, it reaches its maximum effect at 170 on the scale of 0 to 200 as used for the cyan and yellow filters.
Perhaps someone else has the maker’s explanation for this. For practical purposes, it doesn’t matter, so long as you can find a setting that gives you the results you want.
Under
SPECIFICATIONS, My LPL 7700 owner’s manual lists the filtration range for the 670MXL dichroic head as
Yellow 0 – 200; Cyan 0 – 200; Magenta 0 – 165 (not quite 170)