I personally prefer option A, because otherwise the network will be full of bad flips.

Let's say you are a human which has about 700 DNA as reward for the last validation. In the first scenario if you make 1 bad flip you will lose all your reward and next time will create better flips. In the second one you'll just lose 15 DNA, which is tiny 2% of your overall reward. You may even don't notice such a penalty and will continue to make bad flips.

If you want some trade off I would suggest the third option C:
C. 1 bad flip = 20% of overall reward unpaid instead of 1 flip reward unpaid like in option B. 20% means 1 flips out of 5 is bad. 40% means 2 out of 5 are bad, etc.