Excellent but fits a bit small - Vivobarefoot Primus Trail SG Trailrunning Shoes - Women's

I ordered this "SG" (soft ground) model of the Vivobarefoot Primus trail runners to replace my well-worn "FG" (firm ground) model of the same shoe because the SG has a more substantial sole. I loved the shoes when they arrived but I immediately realized that I needed to size up in the SG model because they are slightly narrower than the FG. It might be because the FG has a proper tongue while the SG's mesh material slips onto your foot like a sock. Overall these shoes are excellent but as a general note I have noticed that each model of Vivobarefoots has a unique fit which is why the multiple pairs of shoes that I own from this brand span three different sizes.