(Also reported for Java Edition at MC-249996.)
Explosion damage scales based on how close the damaged entity is to center of the explosion. However, the position of the entity is handled naively, with the result that higher damage is done by explosions centered closer to the entity's feet.

Steps to reproduce

(These steps only show the issue because of MCPE-153740, so if that bug is fixed then you will need to use the alternate steps below.)

1. Give yourself high level health boost and instant health effects so you have lots of hearts.
2. Turn off mobgriefing
3. Make a ghast containment cage of some kind and summon/teleport a ghast inside of it.
4. Switch to survival.
5. Tank shots standing still, and while walking backwards away from the ghast. (Note that if you start to take non-damaging hits, that is a separate bug that can be worked around by changing position slightly between shots: see MCPE-78714.)

Expected result

You take more damage from shots while standing still because they hit near the center of your body.

Observed result

You take more damage from shots while walking backwards because they hit nearer to your feet.

Alternate steps

1. Make fireballs summonable using a behavior pack.
2. Turn off mob griefing.
3. Place a solid block above your head, so that you are standing in a 2-block-high gap between 2 sold blocks.
4. Summon fireballs at ~~~ and at ~ ~1.68 ~

Expected result

The fireballs summoned at ~ ~1.68 ~ do more damage.

Observed result

The fireballs summoned at ~ ~ ~ do much more damage.