Amazon is asking authors to roll the dice and play a game of craps. A few lucky players will win big but the broader community of authors will lose. The odds are controlled by Amazon, opaque and ever-shifting.
Don't let data-driven decision-making cause you to make stupid decisions. If the data shows (and it does) that shorter book titles might give you a slight sales advantage, don't change your title to two words if the absolute best and necessary title is seven words.
On February 18, PayPal contacted Smashwords with an ultimatum: Remove the "edgy" erotica, or face deactivation of their PayPal account. Since PayPal is integrated into the Smashwords website, Smashwords had no choice but to comply.