Fixing window locking wedges

Boohoo

Hello.

I started a thread on MSE about renewing gasket/qlon and window hinges on some old upvc windows.
I have got the stuff I need now and will do the hinges at the weekend.
This week I replaced the old worn out qlon gasket on the side opening casement windows.
The problem I have now is that as they are over 20 years old they close brilliantly on 3 parts of the window but not on the non- handle sides.
After a bit of research I came to the opinion that I need window locking wedges like http://www.ebay.co.uk/itm/White-UPVC-Window-Locking-Wedges-Improves-Security-and-Seal-5-Pairs-/251620478519?pt=LH_DefaultDomain_3&hash=item3a95bfce37
I have ordered them but on the frames they have a rebate part like where the hinges fit but on the open window its flat.
can somebody how I can fix these so the pull the sash in when closing the window please.