The 3 little piggies experiment

A few weeks ago I had some time to spend and I entered one of Etsy community chats. People discussed each others work and while talking to fellow craftsmen someone asked me if I could do a funny pig sculpture. I thought the idea was intriguing so I made a little pig experiment. A sculpture of a pig holding an apple - about three inches tall. (largely using the same technique I use for my Easter/not easter/funky bunnies. Turns out it works pretty good for a pig too. Then I made a small piglet - a really simple one to make, about one inch tall. And finally a magnet that looks like a pig. I am not particularly interested is pigs, so I put them on sale.
Anyway the one thing that was really interesting for me, or should I say became interesting is the magnet/polymer clay weight ratio when making a magnet. The piglet magnet holds easily one a4 piece of paper on my fridge. But it wouldn't hold more paper. The magnet I used was bought from a craft store. It had no description, so the only way to determine how much clay to use in order to have a functional magnet and not one that is useless was experimentation. I wonder if there is another more 'scientific' way to tackle this issue. Please if you know of one tell me.
Boris