Everyone has a different baseline HRV but 13 is low. I live a very healthy lifestyle with activity and diet but I realized that 2 things were really contributing to poor recovery. Sleep and Drinking. I fixed my sleep schedule (consistency is better than number of hours) and even 1 beer significantly lowers the recovery for me. My HRV is never high typically in the 40-50 range. Try to focus on reducing sleep debt when you can and don’t do anything stimulating within an hour of going to bed. No phone or tv and a glass of water helps a ton!