When a TARDIS is either materialised or summoned on top of a default Minecraft half slab which is in the top half of the block, the TARDIS lands at the height of a bottom half slab (images 1 and 2). However, when a TARDIS is materialised or summoned on top of a Dalek Mod half slab which is in the bottom half of the block, the TARDIS lands at the height of a top half slab (images 3 and 4). All other slab positions are fine. DM Update 57.1.0