You can use anywhere you would inject with a syringe, I've seen infusions set positioned on the side at the back, back hip area, goodness knows how the reached that far around, I know I couldn't.. Basically has long as it got fat layer...
But as you say you are slim, have you double checked that the failur's you'll suffereing aren't because the cannular is getting kinked because it touching the muscle underneath the fat layer?? This is more common with 90 degree sets, but can happen with the 45 degrees as well, if the cannular is near enough to the muscle it can restrict the flow of insulin, and the pressure built up with the restricted flow can also cause an occulsion..
Another thing is to check batch numbers, as it could be a dodgy batch (not unknow with the silhouetes) so give customer services a phone with the batch numbers...
I use a telfon cannular as it more flexiable which helps prevent kinks of the cannular when it hits or contacts with the muscle