Small text is indeed one of the fail cases, and more research needs to be done here (see also my other comment [1]). We mention this issue in the supplementary materials [2], and you can check out an example here at [3]
[1] https://news.ycombinator.com/item?id=23654161
[2] https://storage.googleapis.com/hific/data/appendixb/appendix...
[3] https://storage.googleapis.com/hific/userstudy/visualize.htm...