Hmmm. How about this, each side builds a scaleable fleet.
First round, Player A has 2x the fleet they picked, and has to delay Player B with 3x the fleet for as long as possible.
Second round, Player B has 2x the fleet, and has to delay Player A which has 3x the fleet.
So each design has to be able to survey and delay an enemy survey, and whoever does the best combined job at that wins.
And for a roleplay reason explaining this, its actually a Naval design contest for the purpose of solving strategic problems related to survey fleets. They want to know what options to pursue, and how those will fair against other choices other space faring nations might choose.
In a larger contest, with 6 or more contestants, the fleet designs would be fixed at the start, but on entry to the system they would only know if they had the larger fleet role or the smaller fleet role, and not who the opponent was.
Of course, some sneaky judge might decide to put two of the 3x fleets against each other, or two of the 2x fleet against each other.
I think I would still like to see a nodal response scenario, where players can make tradeoffs between the size of the initial fleet and the first two reinforcing waves, as well as tech vs reinforcement size. But that is complicated enough without a survey based I WIN condition.