The other thing, William, I don't know if the current MP works for setting up heli with 3.2.1 anymore? It used to be that you captured the swash range and I think what I would do is manually set your H_COL_ min/mid/max params manually to prevent issues with MP maybe not working with the older firmware. Or if you have the old version of MP, use that instead of the current version.
If you can get H_COL_MID set to be about 5 degrees of collective pitch at close to mid-stick**, H_COL_MAX to give you 10 degrees positive, and H_COL_MIN to give you 8-10 degrees of negative, it should work. These must be set with H_SV_MAN set to the proper number for each setting, and they did not take effect unless you follow the instructions in the wiki on how to "cycle" H_SV_MAN to get it to take effect.
Then just set your H_STAB_COL_MAX and H_STAB_COL_MIN params to limit how much collective pitch you want in Stabilize flight mode. Do not limit the negative collective with the H_COL_MIN param.
I would recommend setting the H_STAB_COL_MIN to give you maybe -2 degrees, and H_STAB_COL_MAX to about 8 degrees, and this must be set in Stabilize flight mode by just moving the stick. And again, I don't think they take effect without writing the params and rebooting the APM, or "cycling" the H_SV_MAN param.
I think once you get your collective pitch range sorted, you will have lots better luck with your collective control.
** The "trick" to getting this set in 3.2 is to adjust the swash linkages and HS_x_TRIM values to get that desired ~5 degrees of collective pitch at mid-stick in Stabilize flight mode. H_COL_MID should always be the zero pitch range. But you want ~5 degrees at mid-stick in Stabilize to get smooth transition to Alt Hold. So in the end actual zero collective pitch in Stabilize will be achieved at about 35-40% stick position