Humanoid Avatar Muscle Pose Issue

Hello. I'm working with a group on students on a university assignment and we've found an issue that we just can't seem to solve!

What we are trying to make is a character riding a unicycle. As we have no animators in our group, we thought it would be a cool idea to use IK's to position the feet at the pedals.

The problem we are having seems to stem from converting it to a humanoid avatar. When looking at the Mapping tab, everything appears to be working fine:

Mapping tab info:

Spoiler

But when I move over to the Muscles & Settings tab, the entire rig is moved down like this:


Which when running the game results in this:


This is the hierarchy for the rig in the inspector:


We're not really sure why this is happening. Is the avatar configured wrong? Is the model rigged incorrectly? Is there something else we've missed? Please help us!