at the beginning of the season the groundsman will ask you how big you want your pitch. I dont think you can change it during the season. but you can find your pitch size at: information---facilities---pitch dimensions
are you for real?? maybe you should get some better players or follow the instructions a little better then, here is some proof that the defence is not that horrible 84 goals for and only 9 against me in 23 matches:
this tactis really working for me bro!! (playing with AJAX Amsterdam) its great and if u ever need help with testing more defensive tactics plz let me know. i started testing this tactic during the season, so my field size is still set at smallest but well its already working good :) thanx again...