Partial retreats optional rule

[TheGrayMouser]

As a newbie to this era I am struggling to understand what effect this rule has, or what effect it doesn't have. I think the manual gives a rather unclear explanation, but maybe I just need to have another cup of coffee, can anyone clarify?

From the manual:
"Select Partial Retreats to allow some units to retreat from a hex after being defeated in melee even when there is not enough room for all of the units to retreat. See the Design Notes in the User Manual for why this is not a default"

and the user manual design notes it says: 

...The dynamics of this situation is known as "choking" and results in greatly reduced
flow through openings. Based on this, there is justification for concluding that
obstructions to their retreat would often result in the surrender of the defeated
troops rather than some optimal reduction.



So does selecting this optional rule make it less likely that a unit unable to retreat due to over-stacking would  be eliminated, or more likely?

Not sure if you have discovered the subtleties of these rules yet and the manuals give hints but not a full picture

* No Melee Elimination and Partial retreats should not be used together ( dire warnings in the manual)  either both off or one or the other...

* Weak ZOC on or off will have varying effects on NME or PR selected

best as I can determine order of the most carnage /least slipperiness of a defending units in a hex:

* Weak ZOC OFF neither NME or PR selected
units cannot retreat if the the only hex open to retreat has an enemy ZOC exerted on that hex, or if a friendly unit in adjacent hex with no ZOC exerted on it and there is no overstacking situation.
*Weak ZOC OFF and partial retreats ON
only situationlly helpfull for the defender( if they could retreat if not for an overstacking situation) because if the escape hex for the retreat occupied by friendlies is in an enemy ZOC, they cannot retreat anyhow and the rule wont apply.
*Weak ZOC OFF, NME ON
If Units cannot retreat due to ZOC's or being blocked they only take the casualties inflicted and they will need to be battered down until "naturally" reduced to zero men.

Its harder to rank the  next three options as its more situational
*Weak ZOC ON and PR on
units has several option of retreat , it can retreat into a friendly hex in an overstack situation and SOME men can escape or
in a no overstack situation it can retreat into a friendly hex even if ZOC'd or a vacant hex, even if ZOC'd..
This one allows the defender to be very slippery...
*Weak ZOC ON, NME and PR off
The only way to eliminate an enemy in one attack if it is blocked on all 6 sides, or if its an overstack situation
*Weak ZOC ON NME ON
the unit can always retreat unless its an overstack situation or surround on 6 sides.  You must batter the unit to zero if it cannot retreat.
Less slippery in getting the defender to MOVE if PR is on , yet the most annoying to eliminate the defender....

For Ren I prefer Weak ZOC OFF and neither NME or PR selected, although PR seems reasonable with weak ZOC off as well
There is nothing worse