In Patch 10.0.5, Blizzard fixed polearms to sit higher on your back when sheathed.

The fix has been retroactively applied to all Dragonflight and Shadowlands polearms. However, polearms from expansions before that will be updated in a future patch.

Patch 10.0.2 (Live Servers) vs Patch 10.0.5 (PTR)