VOX Not Engaging All the Time

VOX question.  What am I missing ?  Since I got my 6500 about 2 yrs ago it has been used for digital and CW modes only.  I just thought I’d get it set up for SSB before having shoulder surgery. 

I have been trying different mics I have here and using the XVERT / duplex port method to set up the mics audio, which has worked well.  PTT is fine, and VOX, well sometimes.  Might work one min and not the next.  Happens with all the mics.  Also happens with both the MIC setting, and the BAL setting using a TRS connector with a TRS Mic.

Windows 10 current.  SSDR 2.5.1  VOX gain as much as needed.  Mic gain between 60 % and 90 % depending on mic.  Mic level, as much as needed but kept out of the overdrive output level.  Delay, short.  Power output, XVERT port ( low ).  Does not matter if the processor or EQ is in or out. DEXP, only as much as needed.  

I just feel this is the forest and trees problem.  Could it be just the act that I am using the XVERT duplex setup  ??