Foxtail are 100% genetic. You particular strain isn't known to be a huge producer to begin with. Are you using LEDs and if so how many watts and what kind? Your tricomes tell you when to harvest, I personally harvest at 60 to 70% amber because I like a more heavy high. I wouldn't take any plan past 70% 80% amber trichomes in fear of degeneration of THC. I've grown some sativas that didn't amount much at all in weight, but was some fire ass dank. I've personally never grew this strain but have a partner that has in his didn't amount to anything spectacular in wait either but but was incredible