The max coupons you can get from the snake is 40 per pop (80 total). If you are soloing and not getting 40 coupons per, try partnering with a groupmate as this should give better rewards (i.e you all only have to run 1 barrier ninja, and global buff ninjas will help everyone - eg: mifune for LMC). Also doesnt hurt to a strong groupmate that can easily carry both of you to the 40 coupon damage threshold, the weakest ninja in the group should run the barrier ninja, rest maximize damage.

Only downside is the increased fight time of 10 rounds of fighting for 3 players, but thats the price to pay if you want coupons and cant get it alone.

Did you guys optimize your lineups, or you just mash together 2 individual lineups and expect it to work (i.e, double manual barrier, no element synergy, no global buffers, etc) :P
Your average damage will definitely be less if you're trying to carry someone weaker, which is why this should only be done by those that really exceed the 40 coupon damage threshold...though it might take a couple rounds ti identify where you are. 80k+ power people should be able to farm 40 coupons solo easily. Players being pulled (if they are exceptionally weaker) should focus more on buffing instead of damaging (i.e earth main 2x attack the carry, etc)