Why do the Soft Claws keep falling off my cats?

I just bought the Soft Claws from Petsmart the other day and applied them to my cat and kitten. They seem to not notice them or care that they are there after applying them. After a few hours though 2 or 3 will fall off. I am applying them just the way it says, but can't seem to keep the caps on either of my cats. I have notice though that no matter what size I use I can't seem to get them to sit all the way up to the skin like they recommend. With both of them it seems that the nail itself is just to thick to fit all the way down in side. The length is perfect if I could actually get the nail down in the cap that far. I have tried using a bigger size and even tried modifying the cap by trimming it. Maybe they are falling off because they aren't on the nail far enough? Why won't the nail go all the way down in the cap so it fits like the picture shows? Why am I doing wrong? Someone help!