yeah i have a diesel that only grow foxtails, and that temp doesnt seem too high, and with temps there your humidity is too low, as temps goes up humidity should too as the air can hold more water at higher temps so it will equalize by taking it from the plants as higher levels. this could be your issue, as far as foxtailing increasing yield, like mitten said many times it will increase bud size, but decrease denisty to the point where it lowers yield, along with flavor. Have you had other stresses on the plant during flowering, if you have these can lead to longer flowering times, and when the plant takes longer to finish it doesnt always agree with bud strcture. So if you accidentally had a light leak, or cold night temps, or low humidity through out, this will cause the plant to ripen more slowly, though many times bud structure goes through it normal process of fattening up, getting dense, then foxtailing. like whoever said it could be high nitrogen too, if your running H&G i'd use a tiny bit less A then B near the end of flower for a better ratio. peace, and good luck