Seems like the author is a slow metabolizer like me. Interestingly enough, it seems that the caffeine half life can be shortened by eating broccoli (https://pubmed.ncbi.nlm.nih.gov/17266520/) - by having coffee in the mornings and broccoli with dinner I've been able to enjoy the mood boosting effects of caffeine during the day and still be able to sleep fine.
Sleep quality aside though, I thought my anxiety was due to stressful job, but maybe it's due to all the caffeine I have in an attempt to be productive.. perhaps something to experiment with myself.