I had this when I was trying to grow outside in a very small greenhouse. I changed the lighting, tried LED, CFL, a whole range and the pitches still remained very small. I introduced a Humidifier, and noticed the pitches started to develop and form much faster but still many didn't fully develop, but I could not maintain my humidity without keeping the Greenhouse completely sealed. For me it was a catch 22 as I then had temps inside the greenhouse higher than 35 degrees midday and even with a huge industrial fan, i could not keep my temps at around 20 - 25 Degrees, so I had to try another plan