Better police roadblocks + chases.
3* - minimum 2 regular police cars with 4 police peds + spikes
4* - minimum 2 SWAT riots with full passengers (8 SWAT peds) + 1-2 regular police cars with 2-4 peds +spikes
5* - 1 SWAT riot (8 peds) + 1 SWAT insurgent gunner (9 peds) + 1-2 regular police (2-4 peds) + spikes
6* - 1 army insurgent gunner with 9 peds + tank + APC.
But even if the wanted level would be high you still would meet different type of roadblcoks on your way for example at 4* you still would meet sometimes 3* roadblcok, at 5* you still would meet sometimes 3* and 4* roadblock and at 6* you still would met sometimes 3*, 4* and 5* roadblocks. Making it mor fun.
P.S. Smashing riots, grangers, insurgent gunners with full passengers is so fun))).