Without having access to your specific files, it's impossible to say definitively.

From the GNU tar specifications v1.35:
"Physically, an archive consists of a series of file entries terminated by an end-of-archive entry".

This implies that a totally standard tarball should only have a relative size difference based on the number of files in the archive.

However, from that same page:
"In addition to entries describing archive members, an archive may contain entries which tar itself uses to store information", using labels as an example of entries that don't contain actual file data.

While looking for information about this, I found this article, which contains:
"let's consider a scenario where we have a tarball that is 1GB in size when compressed, and when extracted, the unpacked data is several 100GB. The size difference between the tarball and the unpacked data is 2.32% to 2.38%."

The numbers line up exactly, but the article is talking about a single 1GB compressed tarball vs the 100GB of uncompressed raw data. If you could give more information about your specific case, it would make giving a definitive answer easier.