VB_DEV1 is a time-based child stream of VB_DEV3, with an (underlap) file in VB_DEV1 and (overlap) / (underlap) files in VB_DEV3.
Without -B, the -fo option does nothing. It should be viewed as a modifier of the -B option, as it causes the search to include (overlap) and (underlap) elements above time-based streams. (-B without -fo stops when the first time-based stream is encountered and does not include these elements.) The -fox option is required for the timeBasisStream attribute to appear in the XML. The -o option is required in all cases. The XML emitted via -fx includes the element-ID, so there's no need to include 'e' as in -foex.

C:\Workspace>accurev stat -s VB_DEV1 -o -B -fox
<?xml version="1.0" encoding="utf-8"?>
<AcResponse
    Command="stat"
    Directory="C:/Workspace"
    TaskId="1749">
  <progress
      phase="Scanning for recently touched elements"/>
  <element
      location="\.\src\data\atlas.prop"
      dir="no"
      executable="no"
      id="3219"
      elemType="text"
      size="394"
      modTime="1401372199"
      hierType="parallel"
      Virtual="7\1"
      namedVersion="VB_DEV1\1"
      Real="303\1"
      overlapStream="VB_DEV1"
      overlapInWs="true"
      status="(underlap)(member)"/>
  <element
      timeBasisStream="VB_DEV1"
      location="\.\src\decrypt.c"
      dir="no"
      executable="no"
      id="2646"
      elemType="text"
      size="14518"
      modTime="1397138904"
      hierType="parallel"
      Virtual="9\5"
      namedVersion="VB_DEV3\5"
      Real="16\1"
      overlapStream="VB_DEV3"
      overlapInWs="true"
      status="(underlap)(member)"/>
  <element
      timeBasisStream="VB_DEV1"
      location="\.\src\tran_server.c"
      dir="no"
      executable="no"
      id="3031"
      elemType="text"
      size="19613"
      modTime="1397583942"
      hierType="parallel"
      Virtual="9\5"
      namedVersion="VB_DEV3\5"
      Real="514\1"
      overlapStream="VB_DEV3"
      overlapInWs="true"
      status="(overlap)(member)"/>
</AcResponse>