Bonus question - does anything change if I'm Concealed and there was no Ambush?
In a recent game, this played a role.
PTO, I was the Gurkhas / British fighting against attacking Japanese.
British Turn, I advanced into CC. In the CC-situation, my British unit was Concealed in Jungle.
The VC required me to prevent the Japanese from exiting units off the board and collect CVP.
In this case, I did elect not to attack them. The Japanese had less FP than me. I seem to recall I had a Concealed 447 vs. a Japanese 347. No Ambush.
So I figured, as the CC was initiated by me and not by the Japanese, it would not be Hand-to-Hand.
The Japanese would have his 3FP vs. my 4FP for a basic 1:2 odds ratio. Since I was concealed, he was halved, so 1.5FP vs. 4FP for a basic 1:4 odds ratio. The Japanese would need to roll a 3 or less Kill# to affect me - a very small chance.
I would block movement through the hex. I might even survive Japanese Prep Fire 3FP x3 TPBF x0.5 vs. Concealed = 4.5FP @ +2TEM Dense Jungle in his subsequent turn. I would at least buy time.
Had I instead attacked, it would have been merely at 1:1 odds. My odds for an Ambush were -2 Concealed, +1 Attacker in Jungle, +1 vs. Stealthy, so not exactly good. Had the Japanese ambushed me, he would have attacked Hand-to-Hand with a much greater Kill number.
It might even have been the other way round: The Japanese advacing into CC vs. me.
They failed to Ambush me (-1 Stealthy, +2 vs. concealed, +1 attacker in Jungle).
They were attacking H-t-H at 1:4 (his 3FP halved for my being Concealed, so 1.5FP vs. my 4FP) for a basic H-t-H Kill # of 5 @ -1 being unpinned Japanese in H-t-H.
This gave him 41.7% chance to CR me and 27.8% chance to kill me.
I took the risk, because if I survived, I blocked the path he needed to get forward quickly.