The size of the bubbles on your heatmaps correlate to how many clicks each link received relative to the others on the page.
Just because a very small bubble exists on the page, does not mean that the link was clicked. It may only be that this link was seen, but not clicked, during the selected timeframe.
To see how many clicks a link received in its position on the heatmap, click the bubble.
In this case, the link received zero clicks during the selected timeframe:
In this case, the link received 210 clicks during the selected timeframe: