3353800 - Even after IQ restarted, threads usage 'NumThrUsed' item always shows more than '80%' - SAP IQ

Even after IQ restarted and no other user is connected, sp_iqsysmon 'threads' output shows that 'NumThrUsed' is already '80%'. But sp_iqcontext return nothing at that time.
We want to know how to check the real 'threads' usage at a given time.

Here is example.

   * System specification and SAP IQ parameter & option ;

- 128 logical processor(s), 64 core(s), in 2 chip(s)
- Max_IQ_Threads_Per_Connection = 70
- '-iqmt' is not set

   * sp_iqsysmon shows after IQ server is restarted :

...
ThreadLimit         3770
ThrNumThreads   3769  (100.0 %)
ThrReserved          211     (5.6 %)
ThrNumFree          731    (19.4 %)
NumThrUsed       3039    (80.6 %)

SAP IQ 16.1 SP05.x

In-use thread, Thread usage, , KBA , BC-SYB-IQ , Sybase IQ , BW-SYS-DB-IQ , BW on HANA with Sybase IQ Near-line Storage , How To