What is a fair amount of shield time?

Shield is currently awarded according to the percentage of destruction of the base. It is fair to say, however, that most players care about the amount of loot stolen. So how about setting the shield time according to the amount of loot taken?

Here is my idea: assume you are a TH8 and someone attacks you and takes away 300K of gold, 200K of elixir, and 2K dark elixir. The amount of shield given should be the amount of time necessary for TH8 collectors of the highest level possible and of the maximum number possible to regenerate this amount of loot. Specifically, in this example, a TH8 can have 6 level 12 gold mines, 6 level 12 elixir collectors, and 2 level 3 dark elixir drills. The total generation is then 6*3500=21000 gold and elixir per hour, and 2*45=90 dark elixir per hour. So the shield should be 200/21 or about 9h 30min regarding elixir, 300/21 or about 14h 20min regarding gold and 2000/90 or about 22h 15min regarding dark elixir.

We obviously take the longest of the three, hence the shield should be 22h 15min.

What do you think?

Having free shields that would go up to 24 hours would simply promote passive farming and not attacking which SC doesn't want. DO YOU have a counter for this? (Sorry for weird all caps)