From a structural basis, about a foot behind the front pylons is best. However, you're right on top of the styrofoam flotation block there, so you don't have room for the bag. They're also hard to get to when you're sitting on the tramp. The guys that put them there are using them to dry out the hulls.
As scary as it seems (from a structural basis), the best place to put them (to be used as storage) is about a foot in front of the front pylon.
I had to install one there to repair a broken pylon shoe 11 years ago and the boat is still going strong (with another owner, now).