Membership BOGO

We have a new level of membership for our 17-18 Season - that for every 2 tickets selected at the member price, one is complimentary. 

I set up a pricing rule as follows: BOGO - Mode, price type change to web complimentary - for every 2 seats purchased at the member price, the rule will apply to 1 of those seats. Max of 999 seats. 

I've set this up in the Test environment and when testing various scenarios on our test website - the rule doesn't fire consistently. For example, when I purchase 2 tickets each for 3 events, only one seat is changing to the comp price. 

Another time I tested it purchasing 2 tickets each to 2 different performances, it comped 2 seats in one performance and the other 2 tickets remained at the member price. I need one ticket for each performance comped. 

We have different prices for different events, which makes it necessary for the BOGO to apply PER performance. Should I set up a BOGO pricing rule for each price level so that the rule will fire only for the performances that have same prices? If someone were to purchase tickets to differntly priced events, would the pricing rule not fire correctly? 

I'm not sure what the best way to set this up would be and appreciate any guidance. 

Thanks!