I assume what is wanted here is for the beginning of a chapter to start not at the top of a new page but some distance below the last text of the preceding chapter. There is no automatic way to do this when the chapters are in separate documents. You need to combine all chapters into one document.
[Method 1] If you copy and paste the text from chapter two at the end of the text of chapter one and so on, you will end up with all the text in one story. A lot of work and chance of introducing error. Then, set the para. style for the chapter titles to begin a certain distance below the last text of the preceding chapter. You may need a style to bump the title to the top of the next page in some instances as well.
[Method 2] If you drag the proxies from the pages panel in chapter two and insert after the last page of chapter one and so on, you will end up with each chapter still in its own story. A little less work and less liable to error. Then, add a text frame below the end of the text in the preceding and link it to first text frame of the next chapter. You will then be able to shift the top of the new text frame up and down until the title has the space you want above it.
The script Merge TextFrames from Ajar Productions will combine the text frames into one. There may be other scripts; search for ‘ID merge text frames’. You could then proceed as in Method 1.
If this is a project you are going to be doing over and over, Method 1 or the variant of Method 2 with a script. If it were my project, I would keep the separate files arranged in a book and go back and play with the typesetting and layout to see if I could eliminate the short pages at the ends of the chapters.
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