Minecraft wiki entry for Slab, associated text: Sneaking reduces the player's hitbox height to 1.65 blocks in Bedrock Edition, and so does not allow the player to walk over a bottom slab with one block of air above it, which is 1.5 blocks of space. In Java Edition, however, a crouching player's hitbox is exactly 1.5 blocks, allowing the player to fit through such a gap. A player cannot walk from a block of soul sand directly up to a bottom slab without jumping – this applies not just to soul sand, but to any block 7⁄8 of a block high or shorter, because the maximum step height of the player is 0.6 of a block. The player can walk off a bottom slab while sneaking, because the sneaking prevents falling only when the distance is higher than one half block.