I believe this tee was used too 'train' to hit the low ball/diagonal barrel path.
The Infini‐TEE ™‐The low ball diagonal plane tee.
Might not want to use this tee for all your swing training....just saying. JMHO.
To reach lower pitches, hitters will tilt their bodies and have a more diagonal bat angle at contact. ...
What are the theories on those variables?
That is, what is a healthy body tilt and bat angle, and what are signs that you've got too much or not enough?
How do you coach hitters on this issue to ensure they have the right mix?