There is little you can do to fix "Turn" play. It is to broke. The idea of adding Opportunity Fire to a CW game especially when it replaces normal Defensive Fire is unworkable. It turns the CW upsided down. Instead of a war where defense had the advantage it gives it to the attacker. It would require a significant rewrite of the Defensive AI to make it work. I consider Turn play only useful for multiplayer games since it simplifies the PBEM.
The basic problem with "Turn" handling of defensive fire is that it assumes that the Defenders fire should be halved and used like "Opportunity Fire" in modern games. The flaw in this is that "Modern" games are about movement and CW games are relatively static. The "Turn" design halves the Defensive fire under the assumption that it will fire more than once therefore getting the equivalent of full strength fire over time. This assumption is wrong because the AI isn't smart enough to know when to fire and the attacker can "game" the AI to reduce the fire to at most once and sometimes none. The assumption that one to three OF's is going to cause as many casualties as Phased Defensive Fire is also wrong because Phased Defensive Fire occurs at full strength when the attacker is at his closed point (usually adjacent). OF tends to occur at longer distances where not only is it halved but attentuated by the distance on the fire table. The Attacker can also "game" the OF to cause the enemy to run out of ammo since the AI will happily pop away at maximum distances.
My opinion is the only way to fix "Turn" play is to continue the idea that lead to the "Embedded Melee" optional rule. Add an "Embedded Defensive Fire" where all the Defender's units fire full strength at the end of the Attackers movement. The fire during movement should not cause ammo use. This will make it a true "Opportunity Fire" that will discourage the attacker from excessive movements in front of enemy units. However, it creates a problem for multiplayer games because it like the Embedded Melee doesn't work well for PBEM.
The alternative is to make the game's AI a hell of lot smarter in choosing its targets and firing. The AI would have to trigger fire based on more than just expenditure of movement points within its LOS. It would need to handle fire based on not just stacks but individual units within a stack. It would need to take ammo levels and chance of kill into consideration when determining whether to fire. It would need to have different ammo depletion tests for half strength fire versus full strength. It would need the ability to upgrade its fire to full strength when units are adjacent. It would be very needy.
