A loose crown will only seem too big. And you still have the issue of how is he supposed to wear it.
Unfortunately, fixing the given crown/hairpiece may be the only way to go beyond a full-on new sculpt with new crown (and that will be pricey).
Ray improved the problem a lot. If it is possible to shave down that forehead, angling the hairline so that the crown could sit forward even more cockily, it seems like that could be the best solution... though perhaps daunting for many. But I don't think there is an easy fix. And an oversized crown sitting atop his uncrowned hair-sculpt will look as silly as the current.
Unfortunately, fixing the given crown/hairpiece may be the only way to go beyond a full-on new sculpt with new crown (and that will be pricey).
Ray improved the problem a lot. If it is possible to shave down that forehead, angling the hairline so that the crown could sit forward even more cockily, it seems like that could be the best solution... though perhaps daunting for many. But I don't think there is an easy fix. And an oversized crown sitting atop his uncrowned hair-sculpt will look as silly as the current.