Sorry to disagree GraemeThe magnitude of the AM is so low as to be inconsequential in the physics of loop propagation. That is, there are factors in the physics of the loop that swamp the influence of AM in the loop, so much so that if we ignore the loop's AM, we don't significantly alter the understanding of how the loop works.
Without AM one cannot understand the underlying mechanism of pullback. One can comment what one sees, but one cannot explain (and certainly not simulate) the behavior of the loop in that case.
Merlin