I think your retreats are fine but this covers pretty much everything.Retreats occur after the combat round and attacking units dont get a free shot at defending units.Artillery may retreat. 1 turn is at least a few months so why do you allow them to get stuck and captured? It takes less than a day to “unlimber” your fixed artillery units.
RETREATS
Except for air and naval interception combat, where the defending intercepting units simply return home after one round, after any round of combat, the attacker may decide to withdraw and retreat. If the attacker does not retreat, the defender may choose to retreat. Retreating attacking units do not all have to retreat to the same territory, but it must be from original territories where the attack began. However, when retreating, all units in that territory or sea zone must retreat, if possible. Defending units that cannot retreat (such as air units out of range of a friendly territory, ground units on an island, or evacuating ground units in excess of transport capability) must remain and continue to fight.
Air Units
Attacking air units that are retreating “withdraw†from combat. They return to land during Returning Air Movement. Defending air units have to retreat to an adjacent friendly territory. If no adjacent friendly territories exist, retreating defending air units fly to the closest friendly territory within their flight range. If there are no friendly territories within their flight then these defending air units cannot retreat.
Naval Units
Naval units retreat by “withdrawing” and remaining in the combat sea zone. This may leave enemy naval units sharing the same sea zone. Retreating transports may not unload their units.
Ground Units
Ground units may retreat to any combination of friendly adjacent territories. Defending ground units must remain in the embattled territory and “fight to the death†only if no other retreat options are available. The ground units then take part in the battle. AA guns may not retreat.
Naval Evacuations
Attacking ground units in amphibious assaults may evacuate and retreat to their transports; however, each armor and artillery unit must first be converted to an infantry unit. Defending ground units may also retreat onto friendly transports in adjacent sea zones. Again, each armor and artillery unit must be converted to an infantry unit. In both cases, the evacuating transports may not move, but if possible, they may each transport up to three infantry units to an adjacent friendly territory. Ground units in excess of transport capacity may not retreat.