Occasionally a sweeping advance or similar circumstance will lead to a situation where attackers engage some models in a enemy unit but not all of them. Models in base contact can not move away in their turn, but any unengaged models may move around as normal providing they maintain unit coherency. At the start of the next assault phase unengaged models may move in to help out their comrades as long as the unit did not remain stationary to fire with heavy or rapid fire weapons.
Errata — Chapter Approved: Main Rules Clarifications (v2.0): When unengaged models move in to help their comrades under the Partial Contact rule, they do not count the +1 Attack for assaulting.
Errata — Chapter Approved: Main Rules Clarifications (v2.0): A squad partially in base-to-base contact that has failed a Barrage Pinning test may not move the unengaged models into combat.