Substructure similarity searching v8.5

Hi All,

I am currently trying to relate a fragment set to an HTS set so that if you pick a example fragment it will show you the molecules in the HTS set that contain the fragment as a substructure at about an 80 - 85% similarity as the fragments have some side chains which are not necessarily relevant.

The best way I can think of doing this is having a substructure search with a similarity function but I cant work out how to get it to work.

Any ideas would be greatly appreciated!