I don't have any experience putting a high frequency driver (i.e. the tweet on that coax) that deep in the footwell. Over the years, I've seen those custom molds that put drivers down there so I'm going to guess that others have sussed it out and it is a suitable location. That said, if you run a coax down there as well as a mid/tweet in the door/sail you're going to be messing with your soundstage and imaging.
My $.02
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