I may be wrong about this, since I didn't do any testbeds, but looked at the code instead which  may not do what I said.

Disengagement depends on a large number of factors in addition to what's in the manual. Disengagement is the process that causes the casualties in retreats, RBC (Retreat before combat) and disengagements, although there are slight differences. Airmobile has different rules.

First, there's a chance that you can just slip by, that depends on the following factors.

Special forces can always slip through, riverines have a 90% chance, and the rest of these cases are in the manual I believe.

If you have a big enough Recce scrren (including helicopters) compared to the opforce, then you may slip by. The recce screen includes any recce units in the hex that you are leaving.

If you have a big enough movement allowance compared to the opforce adjacent to you, then you may slip by.

If you fail those, you can still get by, but you'll take damage which depends on the relative gound, recce, air and artillery strength.