As I understand it, petite capitals should be optically aligned with the x-height but small capitals are noticeably taller.
This is how I designed Small and Petite Capitals for Garava Regular
- Small Capitals are nearly 80% of the Cap Height (1145/1434)
- Petite Capitals are equal to the x-height (958 funits)
- Petite Capitals are approximately the same average width as the lowercase.
- The aspect ratio of Small Capitals is similar to Capitals, Petite Capitals have a squarer aspect ratio
- The stroke-weight of Petite Capitals is similar to that of the lowercase.
These are general principles, not design standards.