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