When adding terms to a taxonomy vocabulary, the "Parent terms" scrolling selector list in the "RELATIONS" section only displays 4 items. When dealing with large, complex, hierarchical taxonomies, this makes it difficult and slow to find the parent (a similar complaint).

I would love to be able to use something like the Simple hierarchical select or Client-side hierarchical select widget there, but assuming that's not currently possible, how can I simply display a longer list to make the selection a bit easier?

I am guessing there is a file somewhere containing a setting of "4" (unless that's a default) that I would able to increase to "20" for example. I hunted but couldn't find it.

I'd be interested in an answer, even if it would be a core hack that I would have to redo with each update.