Water dish Size?

The water dish's i supply for my Bp's are those saucers from the bottom of planters. its mabey half inch high and 6inchs around or so.

Should The water dish be larger and deeper so the BP can soak if wanting to?

It's not necessary. But I'm sure it wouldn't hurt anything. None of mine soak and have plenty of room to.

I use what look like dog water dishes in various sizes depending on the snake. Mine are big enough to allow for a soak and high enough that water will not spill all over if the decide to go for a dunk. This being said I don' keep any soakers, just how I like my bowls.

I go to the dollar store and buy these "tortilla keepers" they are the perfect size for my 400-700g balls and most of mine love to soak at least a couple days out of the month. Just have a bowl big enough for the snake to fully curl up in and fill it half full. The snake will use it if he needs extra humidity.
I think they just like to do it.

My ball does not soak, but I baby sat my friends for a few months while she was out of state and hers tried cramming himself in his water dish every time he came close to a shed cycle. So, I guess it just depends on the snake. If you see yours trying to soak, then he needs a bigger one :)
My boa soaks though.