So this is a very good question, it's clear (and good that) you're aware of different model guidance and the trends. Here's my rational for the Seacoast/SE NH when making the map, excuse the numbered list and lengthy thought process!

1. I do use high-resolution guidance, sometimes called "convection-allowing" models. This naming draws ire from many mets given all models account for convection in one sense or another. Lower-res global models parameterize it whereas short-range guidance have the horizontal & vertical resolution to explicitly resolve convective processes. We won't get into hydrostatic v. non-hydrostatic solvers, but that's important too.
2. The slight southerly trend from 18Z yesterday to 18Z today is certainly of interest. It's important to utilize both positive snow depth change (PSDC) & static or dynamic snow ratio data for this forecast. The current 18Z suite (at 10:1 static ratios) has 7-10" through all of southern NH, but the PSDC is barely 3" and closer to my map.
3. Why this difference and my map much lower then? I've closely inspected soundings and it's clear that the above-freezing warm nose makes it to Concord for several hours, keeping precip in/south of there sleet. In addition, the snow growth anywhere south of Laconia is atrocious, with the strongest lift well below the dendritic growth zone (DGZ). So even if we stay barely below freezing above our heads, snowflakes grow poorly and may even be partially melted, aiding to lower accumulations at the ground when its not sleeting. The PSDC maps illustrate this beautifully.
4. The general rule of thumb is for every inch of liquid, 3" of sleet adds up (3":1"). The average liquid expected south & east of Concord is about 0.70". Let's assume at minimum 30-40% of the precip tonight is sleet and the rest averages to an abysmal 7-8":1" snow-liquid ratio. At most, you're looking at 1-3" of sleet/wet snow slop!