ERDAS mosaicPro from 2D view reference layer is not displayed on top

I am having an issue using the ERDAS mosaicPro from 2D view tool. I am using ERDAS 2015. I have two separate Landsat 8 file bands. Band 1 from one date and Band 1 from another date. I have ran the histogram match tool in (Raster Radiometric Histogram Match). I want to “stack”/mosaic the two .tif files to fill in missing gaps.

Image one shows Band one from December 20th. The black blobs used to be cloud/shadow coverage. All black values have been set to “NoData”. Image two shows Band one from April 15th. Same characteristics as image one. I have set image one as the reference layer for the mosaic tool, but image 2 is being placed on top in the output. I tried switching the reference layer, but I get the same result. I have also tried using the Mosaic to Raster tool in Arcmap 10.4 and get the same result. Is there something I need to change in the output properties? Any suggestions?