Split by File Size not splitting correctly

[Monroe County31892731d1i1]

I am trying to break a pdf file into smaller documents. I select to split by file size and set it to 8mb, but it creates 3 documents, one that is 2mb, one that is 3mb, and one that is 10mb. When I chose to split file size by 5mb it again creates 3 documents of those same sizes. is there a fix for this? I don't care how many different files it needs to create, just so long as none of them are larger than 8mb. 

[try67]

Maybe it's not possible for it to do that. For example, if there's an image on a page that's 9MB in size there's no way to get it below 8, unless the quality of that image is reduced.