The Pilot User's Guide, page 185, provides the guidance.
"If your aircraft is equipped with a Dynon Mode-S transponder, a certified GPS navigator or SVGPS-2020, the appropriate ICAO Surveillance Equipment Code is "EB1". The E adds ADS-B credit, and the B1 indicates that you are 1090 OUT."
As to the ICAO surveillance field... I'm not sure that it really matters? ADS-B IN isn't part of the 2020 mandate. Also, ATC won't call you up because you filed EB1 when you're you've got a 470 or a 472. Anecdotally, look at the website for Public ADS-B Performance Reports:
https://adsbperformance.faa.gov/PAPRRequest.aspx. They've removed all selections for reporting ADS-B IN equipage.