changing default location for .ost data file

Hello there,

I'm running Outlook from Office Pro 2019

I use Dropbox as a continuous cloud backup for all work files.  Anything inside my DropBox folder is auto-synced to the cloud. 

Outlook is using IMAP to connect my web host provider/email server.

I want to relocate the  .ost data file from the default location over to my DropBox folder so its always being backed up.  I use Outlook and DropBox  across 3 different computers and want all email data to be synchronized across all 3 computers.  I do not want to rely solely on the email IMAP server at my web host co.  to maintain a backup of 11 years worth of emails.  By the way I am successfully storing Archived email in an archive file in a DropBox folder. 

Sidebar, I created a new data file in Outlook but it ends up being a .pst and not .ost and apparently with IMAP all data files are supposed be .ost so that also confused me.  

Anyway, if anyone has any advice, I'd truly appreciate it.