Let's use VST 140:120 (1:2) BE 100 as an example.
In this case, your position is equivalent of
1: Buy 1 VST 140 + Sell 1 VST 120 put
2: Sell 1 VST 120 put.
When VST drops, #1 above will actually start to make money, because it is essentially a put protection hedge. The max profit you can make there is $20, same as spread. It is usually unlikely to capture that entire $20 profit, however, you could very much capture 70-80% of this spread in a market like this.
When that happens, you can first close #1 with the profit of $16, i.e, 80% of $20 in this example. Now you only have 1 naked put at 120 left.
If VST stays in this area before expiration, you will be assigned at 120, which essentially means you are buying VST at 104.
If VST rallies and market recovers, you get the $16 for free, and in the meantime, the actual VST you already hold also gain value.
