I have both 1/32nd molds with and without collars and have put #2 sickles in them with no problem. If it's not seating right and this is more true with sickle hooks especially the red ones some of them have a longer length from eyelet to bend that ends up inside the head of the jig. Ones that are too long save and try in another mold.
If you're trying to use heavy wire hooks you'll have to put the hook in close the mold and squeeze it hard or hit with a rubber mallet to set a new groove.