I’ve added some restrictions to mobile that will cap the maximum height of the user field section, makes the section scrollable if it’s very long, and truncates each individual user field after 3 lines. So even on the tiniest devices (350x450) it should be somewhat difficult to get your card to overflow.
https://github.com/discourse/discourse/commit/cd5b7109d04722df5c39b2ded9fa4ead6c290ce4