I’ve found a solution. My frames have captions. Click on and select the caption text, right click and select “paragraph”, in the first tab “indents & spacing” of the options window that opens, set the spacing above paragraph to zero. The picture will then be flush with the top of the frame.
What you describe seems to be direct formatting. You will need to repeat it for each caption frame.
It should be preferable to use ‘Styles and Formatting’ (F11, former ‘Stylist’) and to modify the predefined paragraph style used for captions. This will take effect for all captions having one of the predefined child styles of ‘Caption’ or another style created under inheritance from ‘Caption’ without a specific setting for the ‘Above Paragraph’ spacing.
Good point. I was able to do this using “Update style” - ctrl-shift-f11.