Miller, the location of the reticle varies with model in the IOR line.
My 2.5-10x 42mm with illuminated MP8 reticle has the reticle in the 1st focal plane, thus the mil spacing is correct at any magnification. This elliminates one potential error. It is the primary reason I chose this model IOR scope. It is easier and more accurate to range tgts at the higher end of the magnification ring but it is not necessary to be precisely on one magnification.
The 2.5-10x non-illum reticle scope has the reticle in the 2nd focal plane and the mil spacing is correct at 10x only. Most of the new models also have the reticles in the 2nd focal plane whether illuminated or not. On some the mils are correctly spaced at 10x while others it is at the scopes greatest magnification. For info on specific models you should contact either Scott Powers at the Sniper Country PX www.snipercountry.com
or the importer at www.valdada.com.