that can't be a correct statement. If you mean giving away a few cm's relatively to the direct opposing scrummager, it's one of the aspects that tends to work, it's true. But if you're saying, generally, being short is beneficial in scrummaging, then no. Domingo's scrummaging works because he's a little cube. Thick as he's high, wide as he's tall. That physiological density allows him, along with unique technique in world Rugby, to beat the crap out of opposing tightheads, no matter how much huger (well, back before the rule change...).
In absolute terms, I'd say a physique like Nicolas Mas/Rodrigo Roncero is the virtual paradigm for the tighthead position, and in regards to scrummaging.
Much bigger guys like Phil Vickery work too if they have the control, but by default that's my conclusion so far. Of course, this needs to be re-evaluated with the new rules...as guys like Mike Ross or Geoff Cross, or Vincent Debaty on the left side all of a sudden are master scrummagers