Experiment tracking in Segment

We are currently tracking the experiment via Segment event but want to seek advices on what to pass down to Segment. Right now we only pass

exerpimentId

and

variationId

. However, we are likely to expand beyond A/B testing on those who have

user_id

. It might be

device_id

for example. Would it be better to pass all the targeting attributes inside Segment as event properties?

You can join them later, but its easier to pass them in the initial tracking/exposure call