Question:
Movement across a mountain hexside should be +3, not 3, correct?
Answer:
No, movement across a mountain hexside is treated as if the unit entered a mountain hex, ignoring the actual terrain of the hex entered. For example, a c/m unit entering a clear terrain hex, in Clear weather, by cross a mountain hexside would pay 6 MPs to do so. In Winter (Snow) weather it would not be able to enter a clear terrain hex by crossing a mountain hexside, since a mountain hex is prohibited terrain for motorized and artillery units under those conditions. If the effect was an additional modifier, this would be listed as such, as is done with rivers and wadis.
Source:
[Rules Court, TEM 62]
