sea pickles can be placed in croups of up to 4, and doing so increases the size of the hitbox of the block. However, the hitbox does not accurately represent the model, making the player able to float above the shorter pickles in a group or past the edge of others.
additionally, the 4-pickle block is 1 pixel higher than the rest, which means that if you place a block above them and go into elytra mode, you can place 2 more pickles on an existing one, but not the fourth.