Table 9-1, "Size and Reach", on page 474 of the Pathfinder 2e Core Rulebook notes that creatures of a given size category have either a "Reach (Tall)" or a "Reach (Long)". The same page says,
"Table 9–1 also lists the typical reach for creatures of each size, for both tall creatures (most bipeds) and long creatures (most quadrupeds)."
However, "most" isn't especially helpful when the Bestiary is full of creatures like a raptor, which would seem to be a long biped, or a gelatinous cube, which is... a cube. Creatures in the Bestiary don't appear to have a corresponding Tall/Long designation, just the primary size category (Medium, Large, etc).
While most Bestiary creatures have a reach value attached to individual attacks, those values only apply to those specific attacks. The existence of Table 9-1 suggests that any creature which increases in size, through magical or other means, would gain some sort of reach, but this isn't confirmed anywhere else we've found.
For example, animal companions start out Small, but through the use of feats can become Medium, then Large. Will the companion gain additional reach as it grows, given the existence of Table 9-1? If so, how is tall/long determined for that creature for the purposes of deciding how much reach it gains? What about a creature under the effect of Enlarge or Wild Shape?
Given the existence of Table 9-1, how do I determine if, and how, a creature's reach should be modified when its size changes?