Just to clear things up, the only font currently that actually supports the -XX design sizes is Emmentaler. In other words, at the time of this writing, each of the Sebastiano-XX fonts are identical in every way (except for the embedded subtables, but that's irrelevant outside of their usage in LilyPond). The only reason the Sebastiano-XX fonts even exist is because LilyPond expects the -XX fonts to be there. It goes deeper than that, but I won't bore you with the details there (if anyone really is interested, let me know).
Now, in case anyone is curious, LilyPond's standard size is the -20 font, which means it was intended for a 20pt staff-height. Since everyone does their calculations in pt sizes (just kidding), here are the equivalent staff sizes in millimeters (where 1mm = 2.834646pt):
-11: 11pt, 3.88mm
-13: 13pt, 4.59mm
-14: 14pt, 4.94mm
-16: 16pt, 5.64mm
-18: 18pt, 6.35mm
-20: 20pt, 7.06mm
-23: 23pt, 8.11mm
-26: 26pt, 9.17mm
In LilyPond, the font used is based on whichever font is closest (i.e., staff sizes smaller than 11pt use -11 and staff sizes larger than 26pt use 26pt). Technically, you could use any -XX variant you want because the relative scale within the font itself is the same (i.e., based on a 1000 unit-per-em staff height--sorry for the font jargon). The various Emmentaler fonts were designed with different weights so they appear better at their intended print size. None of my other fonts (at the moment) follow this philosophy, but this I intend to change that

.
In regards to Knut's comment, my experience says that the font should be sized correctly in Finale since its fonts (e.g., Maestro) are sized the same within the font. I haven't used Finale as much as other programs, so I could be mistaken.
As a side note, if you look at the GitHub page I point to in that blog post, you will find the original font files which were originally designed for use with Finale 2009, so maybe you should give those a try and let us know how that goes? Here's the direct link:
https://github.com/fkretlow/sebastian/t ... redist/otf. To download Florian's original files, click on the font name and then click on "View raw" and the download should begin.
Just for the record, "Sebastiano" is a derivative of Florian Kretlow's "Sebastian" font. I can't take any credit for its design, only its re-configuration for use with LilyPond. I had to change the name to comply with the SIL OFL license terms.