Again... two things..
1) Not listing a cap is suicidal to game balance, since I've seen a face at a con get something like 17 net hits.
2) The baseline payments are intended to be decent paydays. We balance these things so that groups without Face characters don't get screwed.
3) Extra stuff is outside the scope of Missions. The more you add, the more complicated it gets, and the more problematic it becomes.
4) Don;t over specialize. Again, 5 net hits means, on average, you were throwing 15 more dice than the Johnson. Yes, exceptions happen. But still. 5 Net hits is a freaking lot of net hits. If this isn;t enough for you, then obviously the Johnsons aren't good enough at their job. Rating 10 Emotitoys, Tailored Pheremones, a social adept, and hey, I can start giving the Johnsons street cred scores as well, if necessary.
5) If 5 net hits aren't enough pay for you. Walk away from the run. <shrug>
6) Likewise, shadowrunners are disposable assets. If you demand too much, Mr. Johnson can always walk away as well. The city is full of shadowrunners eager to take on jobs.
7) the other option is I can not limit net hits... But make the bonus for net hits negligible. Your pay is 8,000¥, plus 50¥ per net hit.
8 ) Don't over specialize. If you find that you're capping your hits every time? It's time to start putting points in other things.
<shrug>
This is a topic that's been discussed to death, and I'm sorry, but there's not going to be more to it than this. It won't necessarily always be 5 hits. Sometimes they will offer additional incentives beyond pure cash. But not always.
Bull