figured I'd update this thread with my attempts to work thru this issue. I finally figured out how to manually adjust the web vtt file to adjust vertical position... If anyone wants the specific workflow, post back and I'll go in to the details...
First, let me go in to a little more detail about my specific situation. I'm supervising the restoration of a documentary from the 80's and my original contract included authoring blu-ray and dvd... After much "tsuris" I was able to get Encore 6 working on my mac... as I had a license for Premiere 6 for the mac (not for windows unfortunately). When I was testing caption workflow from Premiere to Encore, I discovered that the position information was not there in the .srt file I was exporting from premiere... but since there really were maybe 20 or 30 places where I needed to adjust vertical position, I figured that manually adjusting vertical position of captions in Encore was doable... (not going in to any of the details of the adjustments I needed to make to get the .srt file to import into encore - not simple).
Now we come to the latest wrinkle... There is a film festival play at the end of January. Besides a live event screened from a DCP, there will also be streaming available which requires captioning... Decided to test the workflow using my vimeo account. Vimeo's interface in many ways is a nightmare. They often change the interface in what seems to me illogical ways with insufficient details available in help... They do supposedly accept web vtt files for captions, but when I did a short test, the captions did not appear. When I reached out to support, it took a couple of days before they admitted that web vtt files with formatting information DID NOT work at all.... great huh? Youtube will accept a web vtt file and in intial tests did reflect the changes I made in the web vtt file to reposition specific captions vertically. Waiting to here from the film festival about their streaming platform and what's possible with the formatting...
So that's where I stand now... if anyone wants specific instructions on how to manually adjust formatting for individual captions in a web vtt file, post back...