Quads are a weird one. Lots of leathery old Vets who are wary of them, but some folks will note how big and easy to reach they are. I'm one of the lucky ones who never had any trouble with the standard Quad shot i.e. upper outer aspect. So I branched out gradually, currently treat each Quad as 3 sites, upper outer, lower outer, and upper front. Not saying that'll work for everyone, but if it's possible for me, it's possible for some. Have not wrapped my mind around using that "teardrop" above the knee yet, maybe in the future. My guidelines here are to keep each shot about 4" away from the others. I am a bit under 6' tall, not LeBron-size, and those 3 sites all stay 4" away from each other. Doing IM shots, I use 23g mostly, 1" pin, usually rotate every 2 weeks cause I have other sites too, just don't see "multiple-quads" mentioned much as a possibility.
I ALSO recognize that not each possible site in most people's strategy will hold the same amount of oil comfortably.