I feel like the pitch size "problem" is kind of a myth (maybe a self-fulfilling one)...the differences are rather small when you consider it's in cubic metres and I am very skeptical a 2.5 metres in each half is what made us play worse in Wembley...
On a serious not though, I feel it's a myth too. Most pitches are 7140 m² and although we have had different results, I think our away form is much too blame.
And if the extra metre at Wembley makes a difference we should get used to it (mentally and physcially) by training there and using our "Wembley-like"-training pitch a lot in the summer.