Both are copied from the Finnish phonemes, since Finnish was a major
inspiration for Quenya. This means that the ⟨iu⟩ diphthong is a
“falling” one – according to Appendix E of The Lord of the Rings, this
is the original pronunciation, but by the Third Age (the time in which
The Lord of the Rings is set) it had become a “rising” one, so I may
change the phoneme later, not sure.