78-80F is perfect for fat buds...I am able to get solid density and fat buds in 90F
1 - Genetics - no matter how well you grow, if the strain/plant is a fluffy bugger by default of genetics, then you will never get solid density.
2 - Feeding - feeding the right stuff at the right times ensure max density.(high PK during mid to near the end of flower, along with enough mag and calcium)