This can be solved by making harder bots pay more after accounting for increased travel time, increased kill time and increased ammo use.
The Sevant Heralds outside TMA net me far better NIC than the Sevant Grunts that are 500m further away.
I can 2 shot the Heralds so that's 700 nic on ammo but I four or sometimes 5 shot grunts, thats 1400 at best in ammo
Herald 500m away
Kernal 5500
Random loot, say 500
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Total income 6000
Outlay in ammo 700
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Profit 5300
Time taken to kill 10s so 530 nic per second
Grunts 1000m away (more travel time but not taken into consideration)
Kernal 6500
Random loot, say 1000
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Total income 7500
Outlay in ammo 1400
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Profit 6100
Time taken to kill 20s so 305 nic per second
I go farm the Grunts these days cos I felt a bit of a douch farming those newb bots but it is costing me serious NIC