INS and misc parameter config

Hi All.
I just wanted to ask about the value/meaning of some parameters I’m not clear on (I’ve consulted the complete parameter descriptions, wiki, and googled a bit, but couldn’t find further explanations that I could understand):
Note - platform is an octorotor (S1000) with 3DR Pixhawk running AC 3.5, MP 1.3.49, TOW about 12 kg; Autotune was performed recently after gimbal upgrade; I’m trying to improve hovering performance in Loiter and Alt-Hold (it oscillates a bit)

  • INS_STILL_THRESH: set @ 2.75; is it OK?
  • INS_USE/INS_USE2: can they be both set to 1? Or only one of the two should be set to 1 and the other to zero? What’s the difference/impact on different settings?
  • INS_ACC_BODYFIX: set to 1; what would be the difference setting it to 2?
  • INS_ACCEL_FILTER: sdefault is 20 Hz; I want to try with 16-18 Hz: would there be any hazards (crash…)?
  • ARMING_ACCTHRESH: set @ 0.75; it seems low enough, doesn’t it?
  • EK2_IMU_MASK: set to 3 to use both IMUs; would it be better to set to 1 or 2 to use only one IMU?
    Thanks in advance for any feedback on this.