The small Odontodactylids such as O. havanensis, O. latirostris, and O. brevirostris only grow to about 6.5 cm and they all have relatively light, streamlined raptorial appendages. They are built more for speed than power and take a lot of small crabs, small shrimp, etc. While they eat small snails and hermits, they cannot handle the more robust ones like an O. scyllarus can.
This is partly scaling since small 6 cm O. scyllarus also cannot break really heavily armored prey, but it is also more than that since if you measure the same size O. s and O. h, the O. s has a more developed raptorial smashing dactyl.
Roy