Pressures will be 10-15% higher with the bullet out there than it is at normal seating length, so charges should all be reduced by about the square root of 1.15, or 7%, for load work ups starting out there.
A lot of benchrest shooters used to touch the lands, assuming it made for the best accuracy. Later, many found their particular gun preferred the cartridge to be shorter so the bullet was anywhere from about 0.010" to o.050" off the lands. Berger says their VLD's generally do best about 0.150" short of the lands, IIRC? Some folks get best results with the bullet bearing surface seated a full caliber into the case mouth, way back.
So, it varies with the bullet, it varies with the gun. Seating depth, like powder charge, is one of those factors you have to adjust to find your gun's sweet spot. The best approach is to try adjusting it with a starting load, so you don't have high pressure issues as you get close to the lands. Once you find it, then start the powder charge work up to reduce the group size further.
If you do systematic load development, you'll find you can often get half inch groups just working with normal SAAMI col (3.340" for the .30-06) that will still fit in your magazine, where the long seated loads may not. Read through Dan
Newberry's OCW site for a good development system. He doesn't mess with seating depth, but his round robin method can be applied to doing that with a starting load before you work out the powder charge. Up to you.