It appears you're using the term "compression ratio" to mean "size reduction". A compression ratio is the ratio (compressed / uncompressed). A 1 kB file compressed with a 10% compression ratio would be 0.1 kB. It seems you're using (1 - compressed/uncompressed), meaning that the compressed file would be 0.9 kB.

On Nov 28, 2015, at 6:48 AM, Peter Tschipper via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:

The following show the compression ratio acheived for various sizes of data.  Zlib is the clear
winner for compressibility, with LZOx-999 coming close but at a cost.

range Zlib-1 cmp%
 Zlib-6 cmp% LZOx-1 cmp% LZOx-999 cmp%
0-250b 12.44 12.86 10.79 14.34
250-500b  19.33 12.97 10.34 11.11