To your original question - should you list 10k or 20k - if you consider all of the transactions suspicious, they ALL must be included in the total. So, 20k it is.
Some folks will tell you that in a kiting case, for example, you'll only report one side so that you don't "double dip." IMHO, that's pure rubbish. But I've been doing AML for too long and have learned to accept that there are certain gray areas where knowledgeable people can disagree in good faith. One of those is what should be included in the SAR total. So long as you describe in the narrative what you're defining as "suspicious" vs. what you've simply mentioned to provide context, and that definition is within reason, you won't be subject to any issues with a knowledgeable and reasonable examiner or auditor.
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CFE, CAMS