InlayModel.addBlockElement() offset parameter

Hi!
I am trying to use a new 2018.3 feature --- InlayModel.addInlineElement in my plugin for displaying text data above the some lines in Editor. So, the question is: what is meant by offset in given context? For example, I want to display my text above line 10 in editor. So : 

editor.getInlayModel().addBlockElement(10,
        false,
        true,
        1,
        new EditorCustomElementRenderer() {
            @Override
            public int calcWidthInPixels(@NotNull Inlay inlay) {
                return 30;
            }

            @Override
            public int calcHeightInPixels(@NotNull Inlay inlay) {
                return 15;
            }

            @Override
            public void paint(@NotNull Inlay inlay, @NotNull Graphics g, @NotNull Rectangle targetRegion, @NotNull TextAttributes textAttributes) {
                Editor editor = inlay.getEditor();
                g.setColor(JBColor.GRAY);
                g.setFont(getFont(editor));
                g.drawString("WOW TXT ABOVE TXT", targetRegion.x, targetRegion.y);
            }
        });

But after this I see my text not above line with number 10 in editor, just above line 1 (picture attached).

So, can you please clarify, what is the meaning of "offset" parameter in InlayModel.addBlockElement() ?

Many thanks!