I have been through with the same thing. Unfortunately we do not have control over it. As you can see, its all about the data, both the lines are falling into same data points. At such point how qlikview will interpret. Also there is no formatting you can do.
What I can suggest you is that- Keep Text as Pop Up. (Chart Properties> Expression Tab)
This is the only alternative. (Hope this will meet your end user requirement)
You can achieve this with a workaround, if you are willing. I use a seperate expression which I set to be an arbitrary value below the first expression, with a white line colour to fake the values below the other values. EG
expr1: first expression = sales
expr2: dummy expression. This is something like
=[expr1] - 300
=[expr1] - max(total sales)*0.1 --so it is in proportion to the highest amount of sales in the chart
Edit the line colour for expr2 in the expressions list as "=white()" to make it invisible and then tick "values on datapoints" under the display options.
Remember to uncheck the values on datapoints for expr1.
Hope this is a satisfactory solution for you!