It appears that I can't get permissions set to rwxrws--- (2770) for new directories.
Preferences-->Transfer-->Upload option is set like this:
Thats 2660 for files but I suppose WinSCP will add the X for directories as set.
New directories just get rwxr-xr-x which is wrong since the group needs write access and others have no business in those folders.
I can enter chmod 2770 xxxxx on WinSCP's command line and this works as intended.
Where am I wrong?