Juniper MX204 - Flow monitoring with logical systems

I saw a similar post years earlier, but there was no clear answer as I didn't find good info in Juniper documentation either.

I would like to gather flow data in a collector and I'm open to any solutions and formats (jflow v9, ipfix whatever). The MX has multiple logical systems configured which makes this difficult. Do you have any recommendation or are you aware of any helpful documentation in this case?