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It is not really possible in a "good" way.
You can defeat the inclusion of these values in the heatmap calculation though, say by evaluating them to look less like numbers. For example, add to your search
| eval Total = Total . " ." You could pick an arbitrary character here to make it not look like a number.
Custom heatmap logic in advanced XML 1 Answer
customize heatmap in advance xml 1 Answer