Surrounded
The following is my interpretation of how Scenario X should be played.
They are also the rules used for this scenario when playing IUF.
Defending groups are denoted as A', B', C', and D'. The attacker's groups are
denoted as A, B, C, D, I, J, K, L.
I

J

K

L

Attacker's 2nd Force: Range 10

A'

B'

C'

D'

Defender: Range 0

A

B

C

D

Attacker's 1st Force: Range 0

Setup and Forces
1. The defender sets up normally with all his groups starting at Range 0.
2. The attacker must divide his men into two Forces. 1st Force must set up in
Groups A through D (A and B are required); 2nd Force must set up in Groups I
through L (I and J are required). So it follows that the attacker must set up
with a minimum of 4 groups. The attacker is otherwise not limited in the
number of groups it can set up in, up to the limit of 8 of course.
3. All groups in 1st Force start at Range 0; All groups in 2nd Force start
at Range 10.
4. A Force cannot contain more than 1 LMG. The American BARs are not so
restricted since their order of battle vs. the Japanese includes 3 BARs.
Note that the restriction on more than one BAR per group still applies.
5. Groups in each Force are never considered to be adjacent to each
other even if they are at the same Range. So it follows that individual
transfers can never be performed between such groups. The only possible way
that men could be transferred from one Force to another is if they both
infiltrate the same group which is then later eliminated (via the standard
rules allowing transfer of men in such cases).
Movement
1. Note that at the start of play, groups I through L must move backwards
in order to close with the defender. Relative Range, as always, is determined
by adding the Ranges of the two groups in question; if the sum is greater than
5 then this number must be subtracted from 10. So it follows that at the start
of the game the Relative Range between groups A' and I is 0 (0 + 10 = 10 and
10  10 = 0). When group I plays a backwards move its Range will decrease from
10 to 9 so the RR now becomes 1 (0 + 9 = 0 and 10  9 = 1).
2. Note that a defender's group moves forwards to close with the attacker's 1st
Force (groups AD); it moves backwards to close with the attacker's 2nd Force
(groups IK).
3. Red Movement cards are not required to move backwards. This applies to
both players. At Night, observation is not required to move backwards.
4. A group cannot move in a direction that would put it further than RR0 to
the nearest enemy group. So it follows that groups I and J cannot move forward
on the first turn of the game; likewise neither can groups A and B move
backwards on the first turn.
5. A defender's group can be blocked from both in front and behind. For example,
if group I moves backwards to Range 5 (Assuming A' stays at Range 0), group A'
could not itself move backwards because it is blocked in that direction. If
group A now moves forward to Range 5 as well, then group A' will be unable to
move either forward or backward. An attacker's group is not blocked by the
presence of a friendly group from the other Force, so for example group A can
move through group I.
Natural Flanking/Encirclement
1. Per standard rules, natural flanking/encirclement always involves two groups
belonging to the player who is to benefit from the flanking/encirclement. In
this scenario, these two groups must belong to the same Force. In order
for a group to naturally flank a defender's group, it must advance beyond
RR5 and an opposing group in the same Force must exist. For example,
groups A and J can never combine to create a natural flank/encirclement though
groups A and B can.
Standard Flanking (Flank Move card)
1. Per Special Scenario Rules, the opposing group required when performing
a standard flank can be in either Force. For example, A can flank B'
if J exists, even if B does not exist. Also note, that if the defender has
groups A' and C' that B' can flank any one of the four attacker's groups A, C,
I, or K!
Special Encirclement
1. Per Special Scenario Rules, if a defender's group finds itself at RR5 to at
least one enemy group from each Force, that defender's group is considered to
be encircled and suffers all consequences. Note that an encircled group cannot
laterally transfer (per standard rules) so if for example group A' finds itself
at RR5 to both A and I, it will not be able to move forward, backwards, or
laterally transfer!
Summary
Think of the scenario as if there were two simultaneous scenarios being played:
one between attacking AD vs defending A'D' and one between attacking IL vs
defending A'D'. When an attacking group in a Force performs an action, ignore
for the moment that the other Force exists. Likewise, when a defending group
performs an action against one Force, ignore for the moment that the other
Force exists. In general, the defender can be thought of as facing towards each
Force simultaneuosly (a Wall on group A' will give that group a TEM of
2 vs attacks from both A and I).