On the desktop, the changes you prescribed did render the result in the picpaste image, but it didn't work for the netbook or the phone screen. Instead, the three input fields were too large and they partially covered the "Stay in Touch" line above them.
I had thought that I'd be happy enough with only the email address field, so I attempted to "Just leave the first/last name field name settings blank." Come to find out, I hadn't put anything in those fields anyway; they're already blank. I'd be glad to erase them if I knew the necessary emendations to the CSS (so long as the remaining box knew how to position itself, as it did with the Feedburner setup).
Returning the CSS to its original condition and leaving those field settings blank in the widget does produce a result in the "mobile responsive" display: only the email field appears there. But the first & last name fields continue to show on the netbook and desktop.
I currently have the widget configured for MailChimp. http://hbcmemphis.org