Thanks for the question. Here are some sources for supporting data:
A BT/Management Today survey asked managers, ‘Where do you have your best ideas?’ What it called ‘office work’ generated a meagre 15 per cent of good ideas. The more productive occasions were ‘At home’ (17.8%), ‘While commuting’ (17.1%) and ‘During leisure activities’ (16.9%). ‘In the bath/shower’ even scored 11.7 per cent. --Howkins, John. The Creative Economy: How People Make Money from Ideas. London et al.: Penguin Books, 2013. Ch. 5, 51. https://bit.ly/2UrqI7n
Ditkoff, Mitch and Tim Moore. “Where and When Do People Get Their Best Ideas? An Inquiry into the Top Catalysts of Creativity.” Idea Champions (website). June 18, 2008. http://www.ideachampions.com/downloads/Best-Ideas-Poll.pdf. “In the office” ranks 35 of 35 places where people have best ideas;
Ryan, Paul. "Eureka! The top 5 places people have their best ideas.” Australian Anthill (website). Aug. 20, 2009. http://anthillonline.com/eureka-the-top-5-places-people-have-their-best-ideas/
Friedman, Ron. The Best Place to Work: The Art and Science of Creating an Extraordinary Workplace. New York et al.: Penguin Publishing, 2014. Ch. 2, pp 42-43, sec. “The Lessons of Telecommuting: Why Employees Are Often More Productive at Home.” Focuses on productivity, but many factors contribute to improved creativity as well.
Hansgrohe SE. “Shower for the Freshest Thinking.” (Press release). April 2014. Article: http://www.businessinsider.com/why-people-get-their-best-ideas-in-the-shower-2016-1. According to this study, 72% of people surveyed report getting their best ideas in shower. That doesn’t prove by itself that people get the MOST ideas in the shower or at home, but it certainly lends further evidence that they do. PDF of press release available through dropbox link: https://bit.ly/3gB4auT and https://www.evernote.com/l/AAGys7S1F-5DfqZw3_nJgrEIQ4bTOiw559k.
Killingsworth, Matt. “Does Mind-Wandering Make You Unhappy?” GreaterGood.berkeley.edu (July 16, 2013). Available at http://greatergood.berkeley.edu/article/item/does_mind_wandering_make_you_unhappy. TED Talk: https://www.youtube.com/watch?v=Qy5A8dVYU3k
Ovington et al., "Do People Really Have Insights in the Shower? The When, Where and Who of the Aha! Moment.” https://onlinelibrary.wiley.com/doi/10.1002/jocb.126