As far as being an e5 INFP personally, I went so far as to attend an enneagram workshop and sit at different "type tables" (specifically 5, 4 and 9) to try to make sure I wasn't fooling myself. I definitely found the type 5s to be the best fit, even if I don't see that an entirely positive thing. Still, identifying as an e5 did make some of the aspects of how I'm "weird" for an INFP make more sense to me and was good food for thought.
As far as self-reporting on typology forums, seems like INFPs self report as 4, 9, 5 and 1 (in decreasing order of frequency). According to other sources, 6 and/or 2 should be more common for INFPs than 5. So maybe a lot of us are deluding ourselves (and after seeing the reported scores on the "social desirability scale", seems like there's plenty of universal self-delusion to go around).