In many Proofing Rips, a 4ft. Scale is printed and then measured. The 'actual' size is entered into the Rip and a Compensation is calculated, that essentially Scales the job (longer or shorter) to adjust for the difference between printed and measured (actual) size.
So, if the the Job printed one half inch short (in the feed direction) the job would be increased in size to compensate. The Rip does the Calculation. But, if you print that same scale again with the Compensation applied; now when you measure 4 Feet Scale, it measures 4 Feet.
Try to [manually] increase/decrease the length of your job in Photoshop, just before Printing and see what you get. You can still benefit from Printing a 4 Foot Scale and measuring the difference to see how much the print is off — as a starting point
Even if you make your scale a little longer [or shorter] to simulate your typical size, better one of these then many wasted prints