Here is a proposed mechanic for "entrepreneur" NPCs - the ones who delve for a share of loot. After all, they're coming a long for a shot at riches. The more delvers who come, the less risk - but the less reward.
Paid hirelings are unaffected by this. The more the merrier - and the more that come, the more likely they are to come home safe!
For every share-taking character past 4, availability rolls for share-taking NPCs are at -1.
For example, 7 PCs, 1 NPC ally, and 3 hired hands are delving. Raggi is currently available on a 9 or less, the Meeposian Brothers on a standard hireling search roll. Seven share-taking characters worth a -3 to these rolls. Raggi is available on a 6 or less, the Meeposian brothers on a search roll at -3.
Notes: These numbers are set based on my campaign, which now has 11 players who have played at least one session in the past few months. -1 past 4 means -7 if everyone shows up, which is pretty reasonable when a share is maybe 8% of the total haul.