I know it is late to answer but for future references ...
$displayParameters.defaultScreen is set to true when you are editing the default values of a customfield in the admin section. I use it to toggle the visibility of controls that I don't want to display while in that view.
As for the other ones, I cannot say for sure but the $displayParameters.noHeader is most likely used by atlassian to prevent the rendering of their velocity macros which generate the code for the header and footer of a field.
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