That's a tough one.
The absolute best way to force every label to display is to use an autocad drawing with labels in it. (don't expect you to use this method)
But I have fought many a fight to "force" ESRI label engines (all of them) to label everything.
Next best method is to create a feature annotation in a gdb, and then show unplaced labels, and move them and turn on the status to placed.
Next best is what you are doing.
Click on every button in the dialog changing sizes (also don't forget to change the document scale up or down a little to manage some of this) and priority levels until you find one that is closer than where you are (far away).
The ticket's status is in "Needs Discussion", they are still working on this and the only way you can use this feature would be to install the patch. However, reading the last post you can see there are still bugs in it and they are "working on it". (in quotes because it's a minor priority and you could be waiting for a while.)
Alternatively, depending on the length of the content you put in there, you might be able to use a background graphic like such:
strokeColor: "#00FF00",
strokeOpacity: 0.7,
strokeWidth: 3,
fillColor: "#FF5500",
fillOpacity: 0.7,
pointRadius: 12,
pointerEvents: "visiblePainted",
//Supported values include “circle”, “square”, “star”, “x”, “cross”, and “triangle”.
graphicName: "circle",
label: "${order}",
fontColor: "#000000",
fontSize: "16px",
fontFamily: "Courier New, monospace",
fontWeight: "bold",
//Valid values for horizontal alignment: “l”=left, “c”=center, “r”=right.
//Valid values for vertical alignment: “t”=top, “m”=middle, “b”=bottom.
//Example values: “lt”, “cm”, “rb”
labelAlign: "cm",
labelXOffset: "0",
labelYOffset: "0"
Best Answer
As determined through Comments, this seems to have been the result of you using Gill Sans font.
To see that this is not an every font problem I ran a test using Arial, and the halos I added looked good both on the map and in the exported PDF file.