I managed to use participation metrics on simple prop variables, but it doesn't seem to work with "hit" segments.
It is an issue when you have a prop that can have many different values and you want the global participation of a group of those possible values.
For example, I use "Purchase (participation)" as a metric, if I use it with prop1, I get:
prop1 = 'abc' => 150 purchases (in participation)
prop1 = 'def' => 10 purchases (in participation)
prop1 = 'ghi' => 50 purchases (in participation)
But if I create a segment based on hits with prop1 containing 'abc' or 'def', or a segment with prop1 containing 'abc' OR prop1 containing 'def' for example, I can't get purchase (in participation) for this segment (NB: as 'abc' get 150 and 'def' get 10, I guess the segment should get something between 150 and 160).