Yes for Kalafina cover album and yes for other composers composing songs for Kalafina. In all their more than 7 years of career, I still yet to find a Kajiura song that fully utilises Keiko's vocal ability. Her improvisation in Door live and their cover of Love love love makes me realize that Keiko actually has quite a wide range of singing technique that yet to be fully used in Kajiura song. She only has the chance to show it in improvisation parts, not in a song dedicated to her (not that there are many of those also). Maybe that is due to the fact that Kajiura herself said that Keiko's vocal range is not on her comfort range of song composing but dammit it's as if Kajiura turns a blind eye to her ability and makes her stuck doing harmony forever.