Hi naizbtr,
This feature isn't possible in HM3 at the moment, but it has been suggested and should be possible down the road after a major HM3 update.
You can only show heatmaps directly on the HUD/Popups in HM3 now by applying the 'statname.heatmap', and you can control the size of the heatmap thumbnails in the NoteCaddy settings.