What each concept detects
Third head tile applies when the drawn tile was already paired and the best discard is that new third copy. A triplet is not inherently bad; it can simply occupy a slot that the current hand needs elsewhere.
Two-pair axis means at least two independent pairs compete alongside useful blocks. One pair can be the head. The other must justify itself as a triplet candidate or be opened into a more flexible shape.
Fixed head means every equally efficient reasonable decomposition preserves the same single pair. The role is settled, so trimming surrounding floaters is usually more productive.
Decision sequence
- Count completed melds, useful blocks, and whether a head already exists.
- Check each pair’s neighboring connections, live copies, and sequence potential.
- Do not split the only viable head merely to chase a triplet.
- With several pairs, assign the less flexible one to the head and let the more connected pair compete for a meld.
- After drawing a third copy, compare keeping the triplet with restoring the original pair and freeing one slot.
Pair value is contextual
Honor and terminal pairs often make stable heads, but a valuable honor, two visible copies, or a central pair embedded in a compound shape can reverse that preference. The useful question is not “which pair is weakest?” but “which pair best performs the head’s job?”
Limits
Special hands such as seven pairs need a different framework. A two-pair label also does not mean a pair must be split immediately; Tingpai Lab assigns it only when the candidate comparison makes that trade-off relevant.