Heart rate update rate on the phone

I have an iPhone iOS 10 app with WatchKit 3 Watch app extension.

Watch app works with HKWorkoutSession

and successfully requests data .heartRate

. The sample is returned every 5 seconds.

A similar query works in a phone app, but it usually returns an empty array of samples, although it sometimes returns a batch of samples representing a longer period of data from hours (like 10 minutes, say). Presumably this is a tactic to save battery on the watch.

Is it possible for the phone app to request heartRate from the HealthStore at the same rate as the watcher app, or for the watch to display data more frequently via HealthKit?

I can get around this by pushing data from the watch to the phone using WCSession

sendMessage(_:replyHandler:errorHandler:)

- but I would prefer that I could just request HealthKit right on the phone.