I'm trying to figure the math out here. With all six heroes, the check is 40 ESPIONAGE, matching Justice Unlimited's 40 ESPIONAGE. That means rolling a DC 10 with no bonuses. With the maximum Omake bonus of +5, rolling a 5 or higher is a success. But rolling 1, 2, 3, or 4 is a failure. On a d20, each result is a 5% chance, so with four results that would mean a 20% chance that we fail the very important ESPIONAGE check.
With only five heroes, the check is 35 ESPIONAGE against our 40 ESPIONAGE. That means a bonus of +2, so with an Omake bonus of +5 we need to roll 3 or higher. Rolling a 1 or a 2 is a failure, meaning a 10% chance of failure.
Unless I'm missing something, it seems like the only way to guarantee we don't get our cover blown is to only bring four heroes.