IMO, not to the extent that seahorses need it...they need almost a constant supply of lots of food, within their immediate area as they are not extremely fast/active. I suppose if you were going to provide in a way similar to mandarins then larger tank = more lr. But since seahorses really are not reef but seagrass sort of animals it is not entirely natural, nor do many (except dwarf seahorses) feed on copepods to a great extent (though other "pods" such as amphipods or things like mysis are a main part of the diet of larger horses).
Seahorses as they are not extremely active, strong swimmers, need low flow (which in a large tank may mean not a lot of turnover), and a relatively high concentration of food in the tank...and possibly lower temps than our reefs. Easier to do in a smaller tank when you are adding food like brine and ghost shrimp and mysis, so, IMO, smaller tanks are more suitable....depending on the species of course. Also whether they are tank bred (and so used to frozen food) versus wild caught (generally need live food) makes a big difference, but they still require a lot of food relative to other fish (very very short digestive system). I am not saying a 55g is BAD in any way, I'm just saying that for many seahorses it might not be the best way to go....and certainly not with other aggressive fast fish. For dwarf seahorses, I've even read that a 10g is far too large!