I kind of dismiss your premise that shorter stems make a bike more twitchy. Reason is pretty simple. If your fit is correct and you are properly weighting your front wheel, and you are on a bike with a short stem, then you are on a longer wheelbase bike. Longer wheelbase bikes on average have slower steering than shorter wheelbase bikes. Most tend to think of stem length in isolation. It isn't the case. Bike geometry...you mention trail, head tube angle wheelbase and weight distribution have more effect on handling then stem aka tiller arm length.