  Models in which scalar field dark energy interacts with dark matter via a
pure momentum coupling have previously been found to potentially ease the
structure formation tension between early- and late-universe observations. In
this article we explore the physical mechanism underlying this feature. We
argue analytically that the perturbation growth equations imply the suppression
of structure growth, illustrating our discussion with numerical calculations.
Then we generalise the previously studied quadratic coupling between the dark
energy and dark matter to a more general power law case, also allowing for the
slope of the dark energy exponential potential to vary. We find that the
structure growth suppression is a generic feature of power law couplings and it
can, for a range of parameter values, be larger than previously found.
