Potion effects such as speed and slowness will affect your speed and FOV, even when not centered on a solid block, but this does not apply to freezing. This means that if you walk on the edge of blocks, the slowing effect of freezing will not affect you, and rapid shifts in FOV will happen if you walk down slopes. Expected is for the speed and FOV to not change when you're not standing on a solid block, consistently with potion effects.