What causes airy buds outdoors?

In future grows the way to get buds denser is to have less grow points on plant. So remove the undersides and inner branches that won't produce much. Lollipopping the whole plant. I do this but maintain a big canopy. This will redirect the growth wasted there to your upper canopy and remaining grow points and buds. When you hit the 2nd to 3rd week of flowering you want to do this to the plant. Hopefully that helps and happy growing 🌱 plus a rich diet in potassium and phosphorus in flowering helps as well in a ideal ph of substrate for absorption.