You can create a control reference, property node, or invoke node of an array element (as opposed to creating one of those items for the array itself) by right-clicking on the element on the front panel and selecting the appropriate option from the "Create" right-click menu.
Alternatively, if you already have the "element" reference from the array, you can use To More Specific Class to cast it to the Numeric class, thereby giving you access to all the Numeric-specific properties (like "Maximum", in your case).
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