When using a selection set for a Contour which includes spot elevations, the generated contours seem to still consider pressure in other elements.
For example low pressure contours are shown near a tank, even though tanks are not included in the contour selection set.
When using spot elevations, an "enhanced pressure" is calculated at the spot elevation location based on the HGL of nearby elements and the elevation of the spot elevation. You can read more about this using the link further below.
Spot elevations will always consider the hydraulic grade at all elements, including tanks, pumps, etc. If spot elevations are included in the selection set chosen in your contour, in turn, your selection set "includes" all other elements nearby those spot elevations, including tanks (by way of the fact that the spot elevations consider tanks).
One possible option you can consider is to use the "Output selection set" calculation option. You could create a selection set containing all elements except for the ones that you do not want it to consider (such as a tank that would otherwise cause nearby spot elevations to show low pressures. To do this, select the elements to omit, right click, choose to remove from selection set, then choose the selection set you are using in the contours. The hydraulic results (including hydraulic grade) at the omitted elements would show as "N/A" and thus the spot elevations would not consider them, and thus your contours would not.
Another option is to omit the nearby spot elevations from the contour selection set.
Using Spot Elevations