I apologize for bringing this up in your thread and hope it actively does not detriment your trade, if anything, I hope if you don't want my offer that someone else might hate me enough that they'll trade with you instead. I don't mean to spam in the least, I simply wanted to make my case for a different rate than what you were offering. With that said, my argument is simple: Global economies set a precedent for different prices than are immediately intuitive. As does the economics of work and value. The concept that 2 copper for 1 tin means we both get 3 bronze bars is nice but I've done twice the work for the same benefit you're receiving.
How about this offer then: Whoever produces higher quality bronze smelts the gross product together for both villages and we receive as much bronze back as metal we put in. IE: I end up smelting the bronze to q70, you give me 50 Bars of Tin, I pitch in 100 Bars of Copper. From this, 150 Bars of Bronze are made and you receive 50 Bronze for the tin you put in and I keep 100 from the Copper I put in. Then neither side has a quantity profit while both sides have a quality/utility profit on their product.