If "large value types out of row" table option is enabled, the table size is increased
If you use

DBCC IND('TestDb', 'Size', -1)


You can obtain the file and page number of the LOB pages (where your "out of row" values are saved)

Now, with that information get a dump fo the page:

DBCC PAGE('TestDb', 3, 938947, 1) WITH TABLERESULTS;




From those results I can see that for strings with 64 bytes or less the record size will always be 84 bytes. For longer strings will be the actual bytes plus 14 bytes (I didn't analyse strings longer than a page)
And the storage engine will try to fit as many of those records in a LOB page.