User blog comment:Bobtherandomguy/the Fertchen Hypothesis/@comment-1463891-20091118000600

Well, "Isabella and the Temple of Sap" basically showed that within the Fireside Girls, Gretchen : Isabella :: Ferb : Phineas.

Besides, as a general rule, the frequency of characters getting shipped together has absolutely *NOTHING* to do with their on-screen interaction or lack thereof. >_>