We don't use eBay for postage.  We have an Aust Post "My Business" account, and their site is all good, (As it should be!)  

Maybe try that out, rather than constantly having to check that your information from eBay is correct.  

We often find that once there is a Third party becomes involved errors can be an issue. This way you are dealing with the "source".

Also, The more you send the more discount you can qualify for, and that might be a good option for you.