Ja, im nachhinein hab ich auch gemerkt, dass das missverständlich sein kann. Denn ich hatte ganz offensichlich ein anderes Szenario vor dem geistigen Auge als du und LastKnight es wohl hattet.
Ich ging von zwei Einheiten aus, die sich direkt gegenüber stehen und gleich breit aufgestellt sind. (Daher waren alle im kämpfenden Glied auch in direktem Kontakt.)
Als ich dann las was LastKnight schrieb wurde mir schnell klar, dass er wohl von einer sehr breiten Schlachtlinie ausging, bei der es wohl einen Überhang gibt. (Da wäre offensichlich nicht jedes Modell im kämpfenden Glied auch in direktem Kontakt.)
Unter diesen Vorraussetzungen müssen meine Darlegungen natürlich verwirren. Daher bin ich dann auf euer Szenario umgeschwenkt und habe auch mit dem Bild einen konkreten Fall angesprochen, damit diese Missverständnisse uns nicht die Kommunikation verhageln. 
Naja, es ist schon ziemlich genau geregelt, finde ich. (Wir gehen jetzt einfach mal davon aus, dass du angegriffen wirst und dein Gegner zuerst zuschlägt.)
Denke, dass dein Gegner und die Positionierung seiner Modelle entsheidet welche deiner Modelle getroffen werden! Davon ausgehend wendet ihr die Regeln nacheinander an:
Schritt 1:
Remove Casualties (Combat) (Rulebook, p. 150)
"Each unsaved wound is applied to the target unit, causing one Wound to be lost. When a model is reduced to zero Wounds, it becomes a casualty and is removed from play. This continues until there are no more unsaved wounds to be applied to the unit, or there are no models remaining to be removed as casualties."
Schritt 2:
Stepping Forward & Closing In (Rulebook, p. 150)
See also: Stepping Forward
"In combat, casualties are removed from the back rank of their unit as normal, even though it is models within the fighting rank(s) that are being slain. Slain models are considered to have been removed from the end(s) of the fighting rank. This represents members of the rear ranks 'stepping forward' to fill gaps, whilst models remaining in the fighting rank 'close in' upon the enemy.
Note that a model cannot attack during a phase in which it stepped forward into the fighting rank. However, any models that remain in the fighting rank after casualties have been removed are more likely to be in base contact with the enemy, having closed in upon them."
Stepping Forward (Rulebook, p. 102)
"Although models are removed from the back of their unit, very often the casualties will have fallen elsewhere, usually in the front or fighting rank. Removing models from the back of a unit represents warriors behind the front rank 'stepping forward' to fill gaps in the front rank.
However, a model cannot make any form of attack (shooting or combat) during a phase in which it stepped forward. It is too busy clambering over the fallen bodies of its comrades."
Schritt 3:
Set Casualties Aside (Rulebook, p. 150)
"It is a good idea not to immediately remove casualties from the battlefield during the Combat phase, but to temporarily place them next to their unit. There are two reasons for this:
Firstly, when it comes to working out who has won the combat, you will need to know how many Wounds have been inflicted this turn. This can most often be quickly determined by counting the number of models removed as casualties.
Secondly, models removed as casualties before having a chance to attack, and models that stepped forward during the current phase, cannot attack. Therefore, the number of casualties inflicted on a unit will often reduce the number of models able to fight back. By placing casualties next to their unit, you can tell at a glance how many models have been removed from the fighting rank."
Schritt 4:
Excess Casualties (Rulebook, p. 150)
"It can sometimes happen that a unit suffers more casualties than it has models in its fighting rank. Should this happen, casualties are removed as normal, representing casualties caused in the rank (or file) behind the fighting rank.
In such cases, and if the unit suffering the casualties is able to make supporting attacks, any excess casualties will reduce the number of supporting attacks."
Schritt 5:
Fight On! (Rulebook, p. 150)
"With casualties removed, check to see if there are any models with a lower Initiative still to fight in this combat. If there are, repeat steps 1.2, 1.3 and 1.4 for those models. If there are no models left to fight in this combat, move on to the next sub-phase."
Wenn euch das für den Anfang zu viel ist, spielt erstens kleinere Spiele (mit weniger Punkten) und nehmt die Modelle tatsächlich vorn weg, wenn sie erschlagen werden. Damit seht ihr genau welche Lücken ihr mit Modellen von hinten auffüllt (und macht das nicht nur theoretisch im Kopf). Diese Nachrücker schlagen eben schlicht nicht zurück. Der Rest (wenn noch einer da ist) kämpft.
