I have the Sony AX/100, similar cams. If you have the settings correct, there should be another folder that contains the 4k video. If you have it on Dual mode, it will create both. I made notes of where the files are located, On the SD card:
4k video – MP4
S:\PRIVATE\M4ROOT\CLIP
HiDef – MTS
S:\PRIVATE\AVCHD\BDMV\STREAM
Low quality 720 video – MP4
S:\MP_ROOT\100ANV01