ttbb shows large shower uncertainties, possibly from shower starting scales, and should be looked at

some of the issues were summarized in Efe Yazgan's talk here https://indico.cern.ch/event/596233/timetable/

although this has been mentioned a few times, and there are open issues, perhaps there isn't enough interest here in Les Houches (?).

If any of you has something specific in mind, please get in touch with the conveners, or edit this page.