I have applied snapshot and or freehand before the mulch and afterwards.
The best results was obtained before the mulches.
Think about the mulch absorbing the a.i. of the product before it reaches the destination of the soil line. Where is the product best effective from? I haven't yet seen results from wind seed control by mulch top applications. The roots penetrate the mulch. You do not get the added effect of control. The particulates do not always seep down to reach the soil.
This kind of runs along the lines of preemerge granules applied to certain grasses with thatch layers. If the thatch is greater than 0.5 inches, the product is absorbed by the thatch and never is totally effective.