Aspect ratio problem on HDR-Fox T2 playing Samsung phone HD video

I've just spent four hours trying to do what I thought was simple task - make an HD video recorded on my wife's new Samsung J5 phone playable on my HDR-Fox T2 with .nts and .hmt sidecar files. I have succeeded apart from one annoying oddity which does, at least, have an easy workaround. I'm not really asking for a solution, but I'm well out of my depth with the intricacies of video formats and it occurred to me that someone might be able to explain what is going on just for my own information.

The problem is the refusal of the T2 to recognise the file as a 16:9 aspect video.

I also have a Panasonic HC-V500 HD video camera, and I normally edit the output of that (H264) with VideoReDo (TV Suite V5) and save it using a profile which converts the audio to MPEG Layer 2 without recoding the video stream. I then use Raydon's AV2HDR-T2 to produce the sidecar files and all works perfectly.

My first attempt with the phone file, using the same process, failed with an error message from AV2HDR-T2 saying 'No NAL SEI units in H264 source video. Unable to create NTS file'. Since it works OK with the video camera files I decided the phone file must be missing the SEI info. I ran it through tsMuxeR with 'Insert SEI and VUI data if absent' selected, as well as 'Continually insert SPS/PPS' selected and aspect ratio set to 16:9.

That satisfied AV2HDR and all seemed to be going well, but when I played the video on the T2 it displayed in 4:3 aspect. If I switch the T2 aspect from pillarbox to auto it works OK so that will do as a workaround, but what I don't understand is why the video camera files play in 16:9 OK with the T2 in pillarbox mode but the phone file doesn't.

VideoReDo and Windows Media Player play it at 16:9 and MediaInfo reports it as 16:9. The unprocessed MP4 from the phone is the same - but plays at 4:3 on the T2 in pillarbox mode.

I could leave the T2 in auto aspect permanently, but then 4:3 stuff (e.g. Talking Pictures films) get stretched and look silly.

Having spent four hours trying every combination and permutation I could think of, I'd love to know what the T2 uses to set the aspect ratio that must be in the video camera files but not in the phone files. Any information would be appreciated.