On an old server we had an escalation graph that would control when cops could escalate. It was quite detailed and would specify what conditions had to be met in a specific situation for a certain type of high end asset to be used. For example, it would say at a fed a ghost hawk could be used if there are 5 armoured vehicles, 1 armed vehicle, or an rpg.
This worked really well as it eliminated any discretion that cops could abuse to use disproportionately overpowered stuff. It also had the interesting effect of creating two kinds of feds. The first kind rebels would use all their best stuff and maybe trigger escalation. The second involved rebels self consciously limiting what they brought to stay under the escalation threshold. It meant that you didn't need to have access to the best gear to try a fed.
The key is not leaving any ambiguous standard for escalation that can be interpreted however somebody wants.