Insertion of Fullerenes to NTs

The energetically preferred graphitic van der Waals gap is aproximately 0.34nm, which means the effective interiour lumen inside a 1.4nm diameter nanotube is about 0.7nm. Nevertheless, it has proved possible to insert C80 fullerenes, which are nominally 0.8nm in diameter, inside such SWCNTs. How can this be the case?