Auto mode doesn't work!
For better or worse, I do not own a HP-1, however, in all of my P25 monitoring of conventional and trunking networks, fixing the P25 mode to '8' gives the best results (lowest error rate) on my x96xt's.
The obvious caveat here is that these comments are only relevant if the HP-1 shares the same P25 demodulation scheme / system as the x96xt's.
I have never liked the 'Auto' mode. Having two identical scanners sitting side by side and monitoring both stable and fluctuating (signal strength) P25 signals, the scanner set to 'Auto' can be seen to hunt up and down randomly, or settle on a high level like 11, with high error rate, while the scanner, connected to the same antenna via a splitter, with the P25 mode set to '8' has zero error rate. This is a very consistent finding at my location with both mobile and handheld versions. Fixing the level to '8' also provides the most reliable (very) weak signal P25 decode too.
It reached the point several years ago, where I simply set the mode to '8' and the P25 'Level' to '200' and just left it there. IMHO, the Auto mode cannot deal with slowly fluctuating signals, let alone fast multi-path fading that occurs when the scanner is mounted in a vehicle or portable environment.
Unless you have two identical radios/scanners, connected to the same antenna, monitoring the same signal at the same time while trying different P25 modes on one radio, you will never know how much these settings alter the error rate/decode quality and therefore which settings are right for you. You will probably just end up going around in circles, because you do not have a simultaneous baseline/reference 'error rate' to compare your changes against.
Of course YMMV