Remember, the settings are maximum values. When posting attachments, SMF looks to see if any attachment is equal to or less than the max individual size. If no, it is rejected, if yes, it checks to see if the number of attachments is equal to or less the the max number. If no, it is rejected, if yes, it checks to see if the total size is equal to or less than the total max size. As long as the total of the 4 pics is less than the max total allowed, it will work the same. For that matter, you could allow 10 pics per post, but the total size would still have to pass the total max size test, regardless of the max individual size.
BTW, I've never seen SMF set to allow the max individual size equal the max total size, but it should work. I have seen a max individual size of 1024, with a total max size of 2048, and 5 or 6 per post. I would try setting the max individual size to 512, as it allows more flexibility.
Thanks
Scott