Heartbeat doesn't include 'circuit stats since last time'

This message is shown every 30 minutes, as per my HeartbeatPeriod.

[NOTICE] Heartbeat: Tor's uptime is xxx hours, with xxx circuits open. I've sent xxx and received xxx GB.

This message is not (and I don't know how to control how frequently it is shown).

[NOTICE] Circuit handshake stats since last time: x/x TAP, x/x NTor.

How can I make the latter message as frequent/infrequent as I like? Can it be merged into the HeartbeatPeriod?

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