Some of the ISICS sites are simulcast, including the
Des Moines area in Polk County, and several others.
However, for the counties that the OP is interested in,it does not appear that Clinton is simulcast, and the other two counties (Jackson & Jones) are showing as conventional, not on a trunked system. There are ISICS sites in those counties, but no one has submitted any talkgroups on ISICS for those counties & their various cities & towns. I would note that the sites in those counties, as well as two of the three sites in Clinton County, use the statewide license for 700MHz channels, so no way to verify specific tower locations, nor to ensure that 'not simulcast' is correct.
There are three ISICS sites listed for Clinton County, The one that uses 800MHz frequencies is a single site, not simulcast. I suspect that the other two sites are not simulcast either, but since they use 700MHz frequencies based on the states license, there is no way to verify that.
The Diamond RH77A is a good antenna, but it is focused more on the Vhf & Uhf bands. While it's certainly not deaf on 700 & 800MHz frequencies, it's not the best antenna for those frequencies.
Have you tried, when time permits, taking your 325P2 into one or both of the adjacent counties, to see how it performs there? If you are only using at home, and if your house has metal siding, or foil backed insulation in the walls, either of those will hinder your reception, especially for more distant transmissions.
I took a quick look at the ProScan file you attached. I did not see anything out of the ordinary or incorrect. Of course, someone in your county, or one of the neighboring ones, would have more insight that I would from quite a distance away.