I'm playing a Sylph in an upcoming game and I was wondering how the Wings of Air racial feat might interact with the Expeditious Retreat spell.
Wings of Air gives the Sylph PC a supernatural flight speed equal to their Base Speed. Expeditious Retreat increases a character's Base Speed by 30ft, but specifically mentions not effecting other means of movement (such as flight). But, since Wings of Air is based off the land speed this restriction seems to be a bit fuzzy.
So my question: since the Sylph's Wings of Air supernatural flight speed is based directly off their base land speed does that mean it can receive the +30ft boost from Expeditious Retreat even though it normally wouldn't?