Highest energy π-like Molecular Orbitals for C9H9+
Orbital 30a is continuous for both phases and is a paradromic ribbon of twist T=2 (more precisely Lk=2)
This comprises T≅1 from the π basis (a delocalized twist) and T≅1 from a tight (localized) twist occurring in the region of the node, and is allowed because σ/π mixing with the C-H bond lying along the C2 axis destroys the node.
Fast forward: For a pure pπ basis, Lk = 1 = 0.73T + 0.27W (π) which means some of the (unfavourable) twist in this system is converted into (not unfavourable) Writhe.

© H. S. Rzepa, 2006-7.