Only catching small crabs?

I'm new to potting and just starting to try my hand with a couple of
fold up pots. On my first couple of attempts in the south east in
some gullys at the end of rocks at low tide I've picked up a dozen or
two small crabs in each pot. Is this a function of being so close to
the shore, the time of year (mid February) or a combination of these?

Any goods tips for picking up decent sized crabs and lobsters? Do I
need to go deeper using a boat? Should I be potting the pots out over
rocks or sand?

Lol