There is a branch up for review that would allow user set launcher widths https://code.launchpad.net/~thiago-nsantos/unity-2d/launcher-width/+merge/79974
Atm not as straightforward as unity plugin to adjust, shows up in dconf-editor The default would be 66, so it appears a setting of 56 is about the same as 38 in unity-3d Would be a good addition to 2d in this or a similar fashion