Shipping behaviour clarification

[taoreflex]

I'm sure I've seen something about this but I've been searching the forum for over an hour without finding anything.

My question is, if I have maximum shipping weight of 31.5kg per parcel with my carrier, what happens when somebody orders 50kg of goods. Will it automatically add a second parcel, one at 31.5kg and a second at 18.5kg and charge accordingly, or do I need to expand the weight ranges. My weight ranges currently stop at 31.5kg, so do I need to add 31.501kg - 63kg, 63.001kg to 94.5kg, etc. (I pay by box up to 31.5kg). I don't have any products whose packed weight is over 31.5kg so there are no issues there.

Secondly, I have limited my carrier shipping options to most European countries because outside Europe the prices are very expensive. My carrier shipping starts at 2kg. Everything under that goes by post but is global as post is relatively cheap to all parts of the world. I have only created weights for the postal service up to 2kg as this is the maximum that can be sent within the UK using 2nd class packet post and is also the maximum for overseas small packets (except books, which I also sell, where the limit is 5kg). Initially, leaving aside the issue of the different maximum weight for books and for everything else (though if anyone has any ideas on that please contribute), I have a similar problem as I have with carrier shipping but with added complications. If somebody orders 2 items, each weighing 1.5kg, I can obviously send them in separate packages. But unless Prestashop takes 2kg as the limit and then starts over for the 2nd item, I would need to extend the rates beyond 2 kg. But then I have a problem if someone orders a single item weighing 3kg because that is over the maximum weight, but the system is going to think that I can send it.

Looks like a lot of Catch 22 to me. Anybody have any wise and wonderful insights to share?

Thanks.