I get it and you're not alone I see that anecdotally from some others when I or others suggest those too. Only way to know for you is to pin one and see you could always pick up a bag and test, pun intended.
A good general rule of thumb or in this case finger, if you can stick your index finger in the area you are going to pin and you actually feel muscle not so far off or under mass layers of fat, you should be good to go. Think delts, quads, thighs, even ventro glute. I am definitely not the norm (ok or even normal) but I have big old hockey players legs (and I love leg day told you I am not normal) and thighs and I have so much muscle/mass in my thighs all over the inner and outer thigh, I can pin 27's in those twice a day for months if I had too. If there's lean muscle somewhere stick one of those in and it will work. It may open up more spots for you to creatively find you like and can use as well. Rotation is important especially the more your are pinning. Obviously hitting nerves or sensitive spots is a thing so take caution, but we all find our spots and kinda know where they are over time.