I agree that home form has been poor since the ground was redeveloped but I don't think the ground is the biggest issue.
The years before were mainly the Sirrel and Warnock eras - I'd say poorer management comes very much into play.
Whether we were playing at the old ground, or the 'new' one, both of those managers I think would have a better record.
Having said that, the new ground doesn't have the feel of the old one though and does have some impact on results.