Sigh. That is a pilot hole - not clearance. Whilst this may work ok for some types of screw under ideal conditions, it's still a bodge to me.
Like I said, the OP isn't making things for sale.
Perhaps I'm the only one taking the time to do it right?
I'm not saying it's the strongest method of joining MDF at right angles - only that if done *properly* will provide a perfectly satisfactory joint in this application.