My experience in sport specific training revolves around rock climbing but I believe the principle may apply to marathon training as well.
I worked through the on-ramp and AOT in “8 Weeks to SealFit” and reduced my climbing volume to recreational levels throughout. With the improvements in mental and physical toughness I was able to climb harder than ever by the end of the AOT…added grades to both bouldering and lead. I would never have predicted this change in climbing performance. And the change was noticed by my peers in the gym.
If you have time before your next event to work through a full cycle of on-ramp, stamina, strength, power, de-load and PR(12 weeks)–with running added only recreationally outside of these workouts I would suspect the 1/2 and marathon distance times will improve.
I would be very interested in your results if you decided to go down this path.
All the best,