just to clarify something I said:
For now, it would be a good idea to put the rhythm indications via text underneath the chords they relate to (of course!) because it might be possible to read the rhythm as meaning the chords below - since there is not much room vertically to separate the related chord/text line from the systems above and below the one you are intending.
what I meant but did not explain very well is that - in the current versions of IRB/Mac editor - we only know of the Text to be entered underneath - reserving above the bar for the alternative chords (changes). So, making any text entries should really apply to the chords just above it - even though it is just as possible for you to have it refer to the chords below.

Another point is vertical spacing, if there is enough room, you can separate the systems with vertical spacers which would make the text area more clearly relate to the bar/chords above but where there is no room, then the assumption would be that the text refers to the bar just above it. At the moment we are trying to resolve a small problem regarding barlines when you use vertical spacers between systems. This should be fixed in a later update.

We are currently discussing rhythm indications and something might be developed later. I will be posting in Support>Help information on rhythm notation soon so have a look there.