Touring - MEC rack bag -- how to attach to rear rack?

Hi y'all. I have this bag and for the life of me, I cannot discover how I am meant to secure it to my rack.

MEC rack pack backpack (http://www.mec.ca/Products/product_detail.jsp?PRODUCT%3C%3Eprd_id=845524441778193&FOLDER%3C%3Efolder_id=2534374302693353&bmUID=1145695784812)

In the photo it shows the straps going up. But how is it held to the rack? There is a small bit of one side of velcro on the bottom of one end of the bag. I have been using the straps to go underneath the rack and then closing them under the rack.

My new tubus rack is narrower and shorter than my previous rack, and it is not stable, and falls sideways. However, I don't think I have ever had the pack on the rack the way it is intended to be attached.

Does anyone here have this bag? Any suggestions appreciated. Ta.

Sitting with it upside-down on my lap, I think I may have discovered its intended mounting strategy.

<off to try it on the bike>

D'Oh! Success! Those straps that go over the top of the bag in the photo -- they loop under the *inside* rails of the rack and then come out the *outside* and then go up and over the rack to fasten at the top of the bag.

My old rack did not have a facility for the straps to go inside -- it was a flat shelf with an opening only at one end.

I am pleased with the way the bag works with this new rack. Much more secure than the previous system, where a velcro strap at the very front did most of the work, securing to the lip of the old rack.

Gratz :)

Don't feel bad, I tried EXACTLY the same approach the first time I mounted a trunk bag. Like you, once I looked at it for a minute or two the light came on and all was well with the world.

SMW