Caption Display - Inconsistent across platforms and devices

Hi all - 

We are having trouble with .srt captions imported into a video in Articulate Storyline and exported to Review 360. Eventually, this course will be a scorm export hosted on a client's LMS. 

I've read all about how to change caption sizes (and can confirm ours are set to 100%) but the issue isn't the size of the captions themselves. The issue is that the exact same course displays the same caption at wildly inconsistent sizes and placements across platforms and devices. We've left the bottom third of the screen free of text to allow room for the captions but this doesn't seem to help at all. 

See attached for 4 examples of the issue, with client information obscured. You can't see it, but these screenshots are all taken from the same timecode, with the same lines of captioning.

• When previewing them in Articulate Storyline, they are large and cover some content. 
• When exported to Review 360 and viewed on a Mac (Chrome), they are perfectly placed in the lower third of the screen, are readable, and do not cover any content.  
• When exported to Review 360 and viewed on a PC (Edge), they display an inch or so below the entire video player, and are pretty small. 
• When the Review 360 link is viewed on an iphone (Safari), they are huge and cover a large amount of text and part of an image. 

We need the ability to export a SCORM package containing these captions, and be confident that our learners can view them regardless of their end devices. 

Is this an issue with .srt versus .vtt captions? Or something to do with display resolution of monitors? If so, it doesn't explain the discrepancy between the display in Storyline vs Review 360 on a PC, since that's the same monitor and operating system. 

 

Any help would be appreciated. Thanks!