as long as soil scientists and infiltration rate are the folks and terms used in the design of such rain gardens, there will be failures. Maybe not 100 percent, but systematic failures should be expected.
Soil scientists are trained to evaluate soils for agricultural purpose and/or for drainfield design. For the former, it's a question of how much water stays in the soil between storm evants (soil water characteristic curves) and for the latter, it's a question of how water enters the soil when the flux is a trickle at a time (i.e., flush by flush a bit of overflow enters the trench and exfiltrates).
If you take porous media and direct water into that porous media in one prominent flux (i.e., stormwater runoff) you will have infiltration for a spell, but the unsaturated soil colum will become saturated (or nearly so). At the point of saturation, the dynamics of flow are based on the horizontal permeability and the gradient of the mound that's created.
This is a much more complicated problem than perc rate and distance to the water table.
(rant over)
f-d
ípapß gordo ainÆt no madre flaca!