Transaction help - how to handle multipe transactions

Hello.

My query looks some thing like this

"Start process " or "End process "
| parse "process *" as pid
| transaction on pid with "Start process" as started, "End process" as ended results by flow
| avg(latency)

What happens is the current app has multiple "Start process " and "End process " messages with same 'pid'. These happen after some interval.

But the avg(latency) seem to give me results with time differene of the very first "Start process pid1" and the very last "End process pid1". This is messing my average calculations. I know each Start/End process happens within, say, a minute. Is there a way to modify my query to consider only the back to back Start/End messages for transaction.

And yes. There are no other message difference to differentiate the repeated messages.

Thanks in advance