[NTG-context] a different, but not zero, blank at the top of a page

Hello, I need advice on blanks at the start of a page. Usually a blank is ignored when it's at the top of a page. You can force it with \blank[...,force], but its value is the same as in the remainder of the text. So, if the blank over a heading is 2 lines, forcing it at the top of the page produces 2 empty lines (not exactly, because TeX uses a glue at the top for line alignment, if I remember well). What I need is a non zero blank at the top, to align the following text to the grid. A solution could be checking whether we are at the top of the page, and choose the blank amount accordingly. How can I make such a test? Massi