Caption position not working

Yes. Be sure you have backups of your project.

In the Project Panel, right click on the caption stream. Modify -> Captions. Under "Target Stream Format," change the "Standard" to Open Captions. In that dialog, also change the pixel size to your needs, the timebase and the Pixel Aspect Ratio as needed. They should all match your sequence.

If you need to change the location (e.g. all to the bottom middle), in the Caption Panel, right click and caption and pick "select all." Then click the, for example, middle bottom square in the grid.

You can change any caption stream to Open Captions; you cannot change Open Captions to anything else.

Also, prior to import, you can change the Import Settings for captions using that button in the Captions panel. 

Stan

Did you intend for these to be Closed Caption 708? 

If I create a 1080x1080 sequence, create Open Captions and set the size to the same, they seem okay.

If I create 708 captions (which have no settings for pixel size), I can get them into frame by setting the lower right location in the grid box.

Stan

That much should work. Can you open the srt in the Caption Panel and/or add it to a timeline?

Please post a screenshot of your Caption Panel and the timeline.

Stan