When I read everywhere on-line that you have to let the steam out to avoid chewy, dense fluffs, I took that as you have to get the steam out as quickly and as totally as possible. So, I began popping with the lid fully seated (to avoid oil and kernels escaping the gaps from a tilted lid), but when there was an inch of popped corn in the large 6 quart pot, I replaced the lid with a screen sieve/strainer. It's diameter perfectly matched the pot and would "snap" in to place. It's inverted bowl shape gave the popcorn all the room it needed and, of course, allowed the steam to escape totally unhindered. I thought I was a genius, simulating one of those movie theater poppers. But EVERY time, the popped fluff was dense and chewy. What was I doing wrong?
After many months of this suffering, I tried the exact opposite. I poured 1/2 cup of kernels into 2 or 3 tablespoons of melting coconut oil and let them both heat up over medium heat (ceramic stove top), doing a quick up/down shake of the pot every 15 seconds or so to evenly jostle and rearranged the kernels for even heating. I kept the lid on the pot during the entire time, aggressively shaking the pot several times after the pot became full to giggle the unpopped kernels back down to the bottom of the pot.
When half full, I tilted the lid to let extra steam out. The result? VERY crispy and light fluffs, just like theater popped! Point of this story? Steamy heat is CRITICAL for crispy fluffs! It will fully escape after pouring into your serving bowl.
The right amount of light oil is also necessary, so that its vaporized splatters coat the popped kernels, keeping room humidity out when cooled to room temp. Humidity is what makes crispy snacks go "stale."