I can never get this straight with 3D?

Because a Component Parameter has a height which is determined by the Z value set on import.

Correct. If I have some minimum, it can be enforced.

There should be examples of making elements thus in the various tutorials at:

If you have trouble achieving a particular effect, upload your file and a drawing showing what you are attempting to achieve and we will do our best to work through that with you.

Note however that the 3D features in Carbide Create are most suited for decorative use, and it cannot be used as a full-fledged 3D CAD program, examples such as:

notwithstanding.

You may want to consider: