[LargeFormat] Plate Holders & Flim Holders - different planes?

[Clive Warren]

A thought struck me as I was thinking about film holders.

The meandering mind turned to thoughts of film planes and ground 
glass backs. It seems possible that a back designed for plate holders 
will not have the same film plane as one designed for film holders. I 
have a Kodak Specialist 5x7 that has plate backs.

Does anyone know if there is a difference in film plane distances 
between plate and film holders?

Cheers,
        Clive