I read the article and noticed you're still using a dbcache setting of 24000.  I'm pretty sure i've read a post bitcoin stackexchange that bitcoin core has s hardcoded limit around 16GB.  Which matches your results of seeing a max usage of 16.7GB of ram.   Maybe you can get that limit increased?  I haven't dug into the code to see if it's an easy change to make before building from source.  Or maybe there's a reason they put that limit on it.