I was wondering why this didn't work for you and saw that you had put the configuration in the wrong spot. Looking back at my example though I realized I missed something. Sorry about that, and I'll correct it here.

```javascript
    gpii.uiOptions.panels.arrayMergePolicy = function (target, source) {
        target = fluid.makeArray(target);
        source = fluid.makeArray(source);
        fluid.each(source, function (selector) {
            if($.inArray(selector, target) < 0) {
                target.push(selector);
            }
        });
        return target;
    };

    fluid.defaults("gpii.uiOptions.panels.increaseSize", {
        gradeNames: [...],
        // top level option
        mergePolicy: {
            repeatingSelectors: gpii.uiOptions.panels.arrayMergePolicy
        },
        protoTree: {...}
        ...
    })
```