Other than a different color case (the HP-1 has a silver face-plate, the HP-2 is black), the only significant difference between the two is that the HP-2 can handle P25 Phase II systems, as well as Phase I and earlier. the HP-1 cannot receive or track a P25 Phase II system.
Phase II capability would be the only thing that would allow the HP-2 to receive more signals than the HP-1.
One of the largest trunked radio systems in IL is Starcom21 which is a p25 phase II. IL state police, IDOT, several municipalities as well as Ameren are using this system. I don't use a HP2 but rather a 436hp which is phase II capable and mainly listen to this system. I listen to Decatur PD, fire and Bloomington/Normal PD, fire and ems which are on Starcom21.