different items different postage charges in same package

I sell plants with different postage charges but sent in the same package.When I list these I am asked if they are to be as part of a discounted postage scheme which I offer. I fill the form accordingly expecting ebay, or is it pay pal, to sort the postage for me. It rarely happens there mostly seems to be a glitch.I am trying to go through each item to see how it has been listed to know what the buyer is expecting but cannot understand how they can see what they are being charged. It does not help that I offer two different discounts one of

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