Homebrew PCBs

The Ultrakeet super-fuser mods sounded interesting: https://ultrakeet.com.au/write-ups/superFuserV2

Especially since the Royal Sovereign CS-923 is of similar design and available for around $25 from Amazon.   Problem is, the CS-923 has three thermostat switches instead of two, and Ultrakeet doesn't provide much technical information (or respond to emails).    The 3 thermal switches are rated at 110, 120, and 140 deg. C and his modification is to replace one of the 2 switches in his Lowell unit with a new 160 deg. C switch to raise the operating temperature.     Does anyone know which one should be replaced?

I think these switches have normally-closed contacts, but if the first one that opens breaks the flow of current (i.e. the lowest temperature), then what's the point of the others?    (One of the two lower temp switches is selected by a rocker switch corresponding to 3 and 5 mil pouches).   This might be a good solution for toner transfer, but simple as it is, I'm a little puzzled about how to increase the operating temp.  Suggestions would be welcomed!

Bob