Performing MNF on multiple rasters in ENVI?

I am performing a forward MNF reduction in ENVI 5.6 on four different hyperspectral scenes (48 bands each). When I perform the MNF on each one, the Eigen values are different.

How should I go about handling this issue?

I considered mosaicking the images together, but apart from it not being best practice (according to ENVI help), you can only mosaic together images with up to 10 bands. Essentially, I am trying to produce a single coherent image with the least correlated bands.