How to? Pre-set _tcfolder on startup when Folders is set Auto-Hide

Is there a way to pre-set _tcfolder by command before "unhiding" the "Folders" view if TCMD is started with the "Folders" view set to Auto-Hide?

I start TCMD with the "Folders" (and "List") view set to Auto-Hide. Since I want to have _tcfolder set to the current disk drive and directory on startup my tcstart.btm includes the following:
iff %_tctab == 1 then
  CDD /T %USERPROFILE%\Documents
Much to my chagrin this doesn't work and _tcfolder remains unset.
TCC  16.00.41 x64  Windows 7 [Version 6.1.7601]
Copyright 2014 JP Software Inc.  All Rights Reserved
Registered to "Me"
[C:\Users\rchapman\Documents]echo %_tcfolder
C:\Users\rchapman\Documents]cdd /t .
[C:\Users\rchapman]echo %_tcfolder
[C:\Users\rchapman]cdd /to .
C:\Users\rchapman]echo %_tcfolder
And, it is not possible to set _tcfolder from the command line with either CDD /T or CDD /TO.

After "Folders" view is opened _tcfolder is immediately set to the directory specified by the "Start In" directory of the shortcut and from then on both CDD /T and CDD /TO work the way they should. i.e. they way I want them to ;)
C:\Users\rchapman\Documents]echo %_tcfolder
C:\Program Files\JPSoft\TCMD16x64
[C:\Users\rchapman]cdd /to .
[C:\Users\rchapman]echo %_tcfolder
Is this WAD :( or am I missing something>
Warning about using TCSTART to change TCC folders: it forces ALL instances of TCC to start there. When a TCC instance is on the right side of a pipe it generally expects to run in the folder of the left side.
Thanks for the reply Steve and the excellent reminder. My tcstart.btm conforms to the recommendation in the Help for TCSTART well before any folder change.
:: Exit if running in a pipe or transient process
if %_pipe != 0 .or. %_transient != 0 quit
You can specify TCMD's startup directory in Options\TakeCommand\Advanced\StartFolder. That might work better.
Vince thanks for the reply. However -
  1. It appears that environment variables (like USERPROFILE) don't work in the Advanced Options Start Folder field so I can't use %USERPROFILE%\Documents there.
  2. When the Start Folder field is set to the full path (e.g. C:\Users\rchapman\Documents instead of %USERPROFILE%\Documents) then _tcfolder is still unset on startup and can not be set by CDD /T or CDD /TO until the first time the "Folders" view is opened.
I don't know if this is an X64 bug, but, with Win7/32, I put this in my TCSTART.BTM:
echo _TCFOLDER = %_tcfolder
And when I start TakeCommand, I get the correct message in the TCC tab regardless of how TC's startup directory is specified (shortcut, option, or the default).
Then I put this in TCSTART.BTM:
echo tcfolder = %_tcfolder
cdd /t g:\
echo tcfolder = %_tcfolder
And when I started TakeCommand, the TCC tab showed
tcfolder = V:\
tcfolder = G:\
and the two explorer panes showed G:\ as expected.
IMHO, TCMD's startup directory option should expand environment variables.
Steve's right. You shouldn't CD or CDD in TCSTART.BTM (unless it's highly qualified).
I don't know if this is an X64 bug, but, with Win7/32, I put this in my TCSTART.BTM: . . .
Thanks for the reply Vince. I don't have an installed TCC 16.00.41 32bit version available (and really don't have time for a dual installation on this machine ;)) but _tcfolder exhibits the same performance as indicated in my original post under both TCC 15.01.58 x64 Windows 7 and TCC 15.01.58 Windows XP using essentially the same tcstart.btm so perhaps there is some other factor involved.
Steve's right. You shouldn't CD or CDD in TCSTART.BTM (unless it's highly qualified).
Both Steve and your point is well taken but I am content to go with the work around provided in the TCSTART and TCEXIT help page:
You can work around these potential problems with the IF or IFF commands and the _PIPE and _TRANSIENT internal variables. For example, to skip all TCSTART processing when running in a pipe or in a transient session, you could use a command like this at the beginning of TCSTART:

if %_pipe != 0 .or. %_transient != 0 quit