Cannot seem to throttle individual cores with hwpstate_intel

Hello, all.

In order to throttle the Intel Core i3-6006U 2 GHz CPU with
four cores in my laptop, I did the following:

  1.  made sure hwpstate_intel is installed by:
      dmesg | grep hwpstate

  2.  disabled package-level control, to control the cores
      individually:
      machdep.hwpstate_pkg_ctrl=0

  3.  executed the following code:

      i=0
      epp=0
      while [ $i -lt 4 ]; do
         sysctl dev.hwpstate_intel.$i.epp=$epp;
         epp=100
         i=$((i+1));
      done

Now, sysctl has:

   dev.hwpstate_intel.3.epp: 100
   dev.hwpstate_intel.2.epp: 100
   dev.hwpstate_intel.1.epp: 100
   dev.hwpstate_intel.0.epp: 0

Yet it keeps reporting identical frequencies for all the
four cores even without any heavy load:

   dev.cpu.3.freq: 1990
   dev.cpu.1.freq: 1990
   dev.cpu.2.freq: 1990
   dev.cpu.0.freq: 1990

Is it correct behavior? I expected cores 1-3 to have a lower
frequency...  Judging by the observable speed and fan noise,
the total throttling seems still to be determine by the
maximum .epp, i.e. that hwpstate_pkg_ctrl has no effect.
How could I verify and (if confimed) fix it?