It does not seem to be stated anywhere how the Parties in a country are ranked if they have the same number of members.
In eUK two parties with the same number of members exist and the ranking seems to be changing for them on a whim on different days?!
As this puts them in and out of the top 5 this has become an important issue (never knowing which will be T5 on any given day).
Please clarify how the ranking should work in this case.