FW 5.6 affected a lot of things, so comparing against something running FW 5.6 might not be a good point of reference.
That said, if you have a bit of experience with fontconfig, you could always feed it a custom config file w/ a matrix size tweak (there's an example of that in the 'extra' fontconfig shards in my fonts hack). That very much feels like hitting a nail with a very large hammer, but it does the job for me
.