Angelo... interesting question. I seem to recall when opening the trunk right after I got it that it opened fully. Now it just pops open an inch or so. Can't really remember for sure! It would be handy to have it open all the way.

Most automotive trunk hardware includes a torsion spring or two to offset the weight of the body panel (making it easier to lift). I don't know how the HCHII system works... but I suspect it's the same. If so, I don't believe these are adjustable. The only alternative would be to install a stronger torsion spring.

Replacement (stronger) torsion springs used to be common years ago when folks mounted luggage / deck lid racks on the trunk. These were used to offset the extra weight of the rack. I don't know if they're still commonplace... might be with all the wings and such folks install these days.

You'd probably have to do some internet searching on this! Good luck.