So the intercalary month makes the date come later seaonally? ad this drops back until another 2nd Adar is needed, I suppose?
They are falling behind, year by year, so the insertion of the extra month is going to follow the ratio when you are dealing with decades, but there are climatic and atmospheric factors that are pretty much random that can effect it in any given year.
The longer time period you are talking about, the closer the numeric ratio is to controlling.