The over four inch figure sounds a bit to far to the rear for a typical forty size trainer. When in doubt always use the more forward figure and I am sure you will find the figure lownnslo indicated is much closer to the mark.

To put your mind at ease 90% of all our aircraft fly well at 25 to 33% of the cord. So just figure where the quarter chord point is from the leading edge and that will be a safe starting point and you can refine the handeling later after flight testing by just moveing the CG aft in small increments.

John