When using the piggybackpack, mobs picked up drastically obstruct view in first person unless you are in a prone position. This has been the case for several versions and persists in version TConstruct-1.16.5-3.0.4.171

With the pumpkin heads your view is obstructed as well but you can still see. Even if they were just high enough so that it only obstructed the top 2/3 of the screen i feel like that would have more parity to Minecraft's other vision obstructing effects. But if this is as intended then so be it.

All the piggybackpack does us make the entity ride you. Minecraft is responsible for where they ride you, so if you can't see blame Mojang.

Are you expecting the mob to float above your head? This is the "down-side" of using it.

Understood. And thanks for taking the time to read it over!