-Hom isn't synonymous with mach and no one said it was. -Hom can refer to diminutive aspects of things besides size (such as importance). But mach is one of the notions that can be expressed with -Hom, and there are examples (bo'DaghHom, naQHom) where it appears to be the only notion expressed with -Hom.

I'm not going to go so far as qurgh in declaring the lack of only-smallness of -Hom, but I do think bo'Dagh may be a special case rendering it unsuitable as a data point here. bo'Dagh'a' and bo'DaghHom are both introduced in KGT as words used to represent exaggerating and trivializing, respectively. It's the -'a' and the -Hom that contain these meanings, not the bo'Dagh. Although the expression is fixed, the fact that it's a spoon is really irrelevant: if the expressions had been taj'a' lo' use a big knife and tajHom lo' use a little knife, the meanings would be just as clear. So the -'a' and the -Hom really do mean something more here than just big and little.

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SuStel
http://trimboli.name