Participation Allocation for Channel Combination

[#1]

Though we usually use Last Touch and other models, I occasionally use Participation attribution to show marketing team the largest potential impact they've had from a channel.  I'm wondering if there's a way to get the deduped Participation allocation of two channels combined.  My attempts at segmenting or calculated metrics to solve these haven't worked.

[#2]

Would you be able to share a specific example of what you are trying to achieve?  If this is visitor based you could use a sequential segment, marketing channel = channel1 or marketing channel = channel2 THEN success metric exists.