Why Your Fabric Affects the Strength of a Snap
The material that the snap is attached to will make a difference regarding how "strong" they hold. That's because when you pull a snap open, you tend to grab on to the material to pull apart. You don't actually pull at the snap. So the weaker the material, the "stronger" a snap will feel. But the thicker or denser the material, the "weaker" and easier to open the snap will feel.
Scenario 1: snap is installed to a thin piece of stretchy fabric. If you pull the fabric apart to try to open the snap, it's likely that the fabric will stretch out and tear at the point where the snaps connect. That's because the fabric is thin and weak. So in this scenario, the snap feels too strong.
Scenario 2: snap is installed to a very dense piece of leather. Even though it's the exact same snap as scenario 1, here the grip of the snap will feel weaker because it's connected to such thick material.
The snap is the same in either case, and technically they have the exact same hold. If you were to open the snap at the snap in both cases, then the grip would feel identical. But because you're using the fabric to pull the snaps apart, that material then becomes the controlling factor in how secure the snaps "feel."
Different snaps can have different grips. But my point in the above is to explain that even the same snaps can "feel" like they have different grips, depending on what they're attached to.