It’s my understanding that fox tailing can be good or bad, genetic or caused by heat/light stress.
The good: genetic; most commonly found in some Sativas from tropical regions. Which would make sense. They’ve adapted to their environment as fox tailing is usually a defense mechanism to help dissipate heat. Plants that genetically foxtail tend to have a higher THC content.
The bad: heat/light stress related. Fox tailing can occur from heat/light stress due to intensity, of which LED or HPS are the most susceptible. In this case, the calyces are focusing on spiral growth away from the normal structure, in an attempt to dissipate heat. This focus on stressed growth can have a negative affect on overall THC content.
Monitoring environmental temps, surface leaf temps, raising the light, or dimming the light can aid in alleviating these stressors if you’re starting to see signs of fox tailing and they’re in fact not genetic.