The lesson on e/er finally showed me why no one understands when I say 河北. I thought the problem was that I made my h too guttural. But really I was not making my e guttural enough. This also helps with se/she/che -- though I agree with the user who thought a lesson on e/i would be more useful than e/er, since e/er don't really sound that much alike anyway. And I would like more help with h. I think you say just a little about that in some lesson but I cannot recall which, and I don't think you said very much. Honestly I would not raise such small things except that S.I.R. is really a terrific series and hope you will expand on it.
Congratulations on your success of distinguishing the /e/ from the /i/ after z, c, s, zh, ch, sh, and r!
And I believe, from now on, you can say all the /e/ better, don't you?