I take the new poppin frog and simply lay the legs along the side of the body and trim it right at the front mouth of the bait or the hook eye as mentioned above. Then you can shorten one leg a 1/2" to make it easier to walk if you desire.
If you trim too short or get one that gets chewed on - it's easy to replace the legs in whatever color you want.
I opened a couple this weekend that were a good bite shorter than normal straight out of the package. Not sure if that is the norm now or not, but I had a couple that were a few months old in the boat and the 2 new ones were much shorter.