where both [Position] and 'LONG' are correct, case sensitive field name and possible value, trying to find out where the problem is. If this doesn't work, please attach some example to see what may be happening.
Bear in mind that you cannot "copy" expression names from a different table to another one, but the complete calculation (the expression) you have written. The formula above equals to saying "show Net Open Position when is greater than zero (Long)" as in your chart above.
To exclude USD from yoru chart, do another expression with