A 173 Correction

No. After the melee touch attack, which gets no special modifiers, and possible AoO the attacker makes a STR check opposed by the defender's STR or DEX Check, whichever modifier is higher. BAB is irrelevant. Every combatant gets a +4 for each size category he is larger than medium or a -4 for each size category he is smaller than medium. The target also gets a +4 if it has more than two legs or is otherwise exceptionally stable (like a dwarf for example)

In your example it is d20 + STR mod for the attacker and d20 + STR/DEX mod -4 for the defender.