Non-Indexed match query should be before or after project?

@Pavel_Duchovny I was trying to keep as less indexes as possible.

My initial indexes were { field1: 1, ts:1 } and { ts:1 }

When I read about cardinality it made a lot of sense to put { ts:1, field1: 1 } instead of { field1: 1, ts:1 }.

My queries are mainly ts range and specific string id of source in field1 OR just ts range. So I figured just { ts:1, field1: 1 } index will do for both.
But now it looks like I should rethink.

I know this is off topic from this thread, but if I go back to { field1: 1, ts:1 } do you think I should add { ts:1 } as well? Or should I first look at the metrics and then decide?