Why is 2,4 pentanedione more highly enolized than 1,3 cyclohexanedione?
Enolization of acetylacetone allows a 6-membered ring, stabilized by hydrogen bonding.
On the other hand, when the cyclic dione enolizes, because the oxygen centres are constrained by the ring, and hydrogen bonding would occur intermolecularly, rather than intramolecularly.
I am trying to think how you would be able to test this hypothesis. Maybe the