Will adding all of my Custom Containers to Shipping avoid overcharging customers for shipping?

Site URL: https://www.gochemtek.com

Hello,

Our shop previously offered free shipping on orders under $100 but we're now increasing this to $200. We have about 15 different box sizes and I'm wondering if we need to add all of the custom box sizes? For anyone else who uses the Custom Containers, are you adding in all of your boxes or just the largest ones?    I know the description says "shipping costs will be estimated at checkout by packing the order into as few of these containers as possible" but I don't know how accurate this always is. Can anyone share insight or experience?

Thanks!