Both sides of a Percentage or Ratio custom metric currently have to come from the same dataset. Choosing a Measure filters the "Over" field to that dataset only.
This blocks any rate that spans datasets, including CSAT survey coverage:
Conversations with a conversation rating request ÷ New conversations
Both count conversations, but one is a Conversation rating metric and the other is a Conversations metric, so the builder won't allow it.
Coverage is the context that makes response rate meaningful — 60% response across 90% of conversations and 60% across 20% are very different situations, especially when you're using CSAT to judge Fin's performance.
Today this only works by exporting both numbers into a spreadsheet, so it can't go on a dashboard or be tracked over time in Intercom.
Request: allow cross-dataset ratios for conversation-level metrics.