If it is an actual flare, and it looks to be from the picture, then there is a separation of the wall from P3. That cannot be corrected in a trim but must be grown down from where the separation starts down to the bottom. One inch up would mean about four months to grow down.
During that time there will be mechanical stresses that will tend to keep the flare going. The mechanical stresses can be reduced by rolling back to the inner wall and reducing the outer part of the flare down to the inner wall. This weakens the wall which lets it flex some and thereby reducing the mechanical stress even more. This is the reason Gene Ovnicek dresses flares from the top. Not for looks but to reduce mechanical stress while the flare is growing out from the top or starting point.
Agree with this, if the flare is due to simple separation, but you are not going to correct way of travel, in a horse this age, and if that flare is due to that hoof not landing flat, due to conformation, further up the limb, you are not going to grow out that flare, but just need to regularity balance that hoof, where the un even landing is causing that flare
There is great tendency, JMO, for many people hat get obsessed with hoofcare, without taking anything above that hoof into consideration, far as hoof abnormalities
I could certainly be wrong here, but reserve thinking all will be well, by growing out a new hoof capsule, until I see that horse travel, or at least better front end confo pics