ماکروی مربوطه که باید تعریفش رو تغییر بدی \floatc@bidituftefloatplain هست.
\makeatletter
\AtBeginDocument{%
  \bidi@patchcmd{\floatc@bidituftefloatplain}{%
        \smash{\hspace{\@bidituftefloat@caption@fill}\usebox{\@bidituftefloat@caption@box}}%
}{%
       \@bidituftefloat@checkoddpage%
    \ifthenelse{\boolean{@bidituftefloat@odd@page}}%
      {\GlobalSetBoolean{@bidituftefloat@float@recto}{true}\@bidituftefloat@float@debug{Detected page: [recto/odd]}}%
      {\GlobalSetBoolean{@bidituftefloat@float@recto}{false}\@bidituftefloat@float@debug{Detected page: [verso/even]}}%
  \ifthenelse{\NOT\boolean{@bidituftefloat@symmetric}\OR\boolean{@bidituftefloat@float@recto}}{%
    % asymmetric or page is odd, so caption is on the right
\smash{\hspace{-\@bidituftefloat@overhang}\usebox{\@bidituftefloat@caption@box}}%
    \@bidituftefloat@float@debug{Caption position: [right]}%
  }{% symmetric pages and page is even, so caption is on the left
   \smash{\hspace{\@bidituftefloat@caption@fill}\usebox{\@bidituftefloat@caption@box}}%
    \@bidituftefloat@float@debug{Caption position: [left]}%
  }%
}{}{}
}
\makeatother