Contact Shadow for a Floating Product PNG

Write the steps to put a believable contact shadow under a product PNG that currently floats. ASSET Product: [WHAT AND HOW HEAVY IT SHOULD FEEL] Surface it will sit on: [WHITE | A KNOWN BACKGROUND] Light in the original photo: [DIRECTION IF KNOWN] Output: PNG with shadow, and a version with the shadow on a separate layer. METHOD 1) The shadow is not a uniform drop-shadow filter. Describe a contact core (darker, sharper, small) and a softer ambient shadow, and which direction matches the product's own shading. 2) Non-destructive layers, multiply, and the blur numbers as a starting point I must judge on screen, not as gospel. 3) How to handle a product that already has a cut-out halo. 4) The check: flip the background to a mid-grey and to black. The shadow should survive both or I should supply two. 5) What not to do: a shadow that points toward the light, a shadow larger than the product on a bright white infinity sweep. If the PNG's light and the new scene's light disagree, say the shadow will not save it.