Place a random unused map adjacent (A2.5), refer to A 2.3 which talks about 1/2 hexes. Measure for an obstacle and enter. Infantry can enter in bypass, why not AFVs?
Per A2.51 ..."All terrain on an offboard setup map is considered Open Ground
except for off-map half-hexes which are butted against a half-hex of some other terrain type and hex rows Y, Q, and I which are road hexes if the board is butted lengthwise. "
So, in our situation, we have half-hexes butted against a woods half-hex, so per the underlined A2.51 exception, the terrain in that offboard setup map half-hex is NOT considered Open Ground.
A2.3 tells us "In the rare instance in which an Open Ground half-hex is butted together with another terrain type half-hex, the combined hex is considered that non-Open Ground terrain type." yet, we just were told in A2.5 that that half-hex of the offboard setup map is NOT Open Ground.
A2.51 does not state all terrain is open ground, including the half-hex portions butted against the onboard map. It does not state that all hexes/half-hexes on the offboard setup map are considered Open Ground terrain. Yet A2.3 is specific in its language regarding what the terrain type of the hex is considered if in those rare instances you get an Open Ground half-hex with another terrain type. Not so rare given every scenario with forces coming onboard across the long side of the board will potentially have the half-hex issue.
I don't think anyone actually thought about it. It would have been easy to state "All hexes on an offboard setup map are considered to be Open Ground. See A2.3 for off-map half-hexes which are butted against a half-hex of some other terrain type."