What is the space between -10 promoter sites and start sites (+1)
By "start site", do you refer to the "start codon"?

I think the spacing you are referring to is the 5' UTR.


  The 5′ untranslated region (5′ UTR) (also known as a Leader Sequence or Leader RNA) is the region of an mRNA that is directly upstream from the initiation codon. This region is important for the regulation of translation of a transcript by differing mechanisms in viruses, prokaryotes and eukaryotes


Have a look at the wikipedia article for more information about its roles.

The 5' UTR is typically 3 to 10 nucleotides long in prokaryotes but can be much longer (up to several thousands of nucleotides) in eukaryotes. On which species did you notice this spacing of about 10 nucleotides?