the rules state you place one corruption on each tile you own in the santurary is that corruption that you had already gained in the game. I'm assuming yes because it seems that you want to have more tiles and in the end of the rules it states you lose a corruption for each tile.
Denmark Aarhus Unwashed and somewhat slightly dazed...
...Or to sum up in unmistakable terms: For EVERY SPACE OF SANCTUARY you have, you get to remove ONE corruption from your pyramid, BEFORE counting who has the most corruption. Remember that, as you use your statues of Anubis to mark your sanctuaries, you can have a maximum of TWO different sanctuaries, each consisting of 1 or more spaces.
And then a little tactical advice: If you keep an eye on what pieces of mosaics have been built, a timely use of a SCRIBE card or two, will allow you to pick the mosaic(s) of your choice, and not just the one from the top of the pile... If you do this, especially if you build TWO sanctuaries at the same time, you will often be able to create really large sanctuaries.