What you experienced is entirely normal. Pressure and velocity generally decrease the further from the lands you load. Reference this chart by Barnes
the blue bars are ball powders,
the red bars are extruded,
the first set of bars above the caliber are at .025" off,
every set of bars goint to the right in that caliber is additional .025" off,
except 300 wtby where they couldn't get close to the lands
The 308 with ball powders shows decreased pressure with increased seating depth
The 308 with extruded powders shows a general decrease in pressure until seated .125" off lands
The 30-06 with ball powders shows a drastic decrease in pressure between .050" and .075" and then a slight increase
The 30-06 with extruded powder show a steady decrease in pressure with increased seating depth
The 300 WSM with ball powder shows a general decrease in pressure with increased seating depth
The 300 WSM with extruded powder shows a decrease until .075" off and then goes back up
The 300 win mag with ball powder shows a steady decrease in pressure with increased seating depth
The 300 win mag with extruded powder shows an increase between .025" to .050" and then a general pressure decrease with increased seating depth
The 300 Wtby shows a steady decrease in pressure with increased seating depth with both ball and extruded powders
The 300 RUM with ball powders shows a steady decrease in pressure with increased seating depth
The 300 RUM with extruded powders shows an up and down but generally steady pressure
The point is that in several of these instances the pressure is reduced with increased seating depth and that seems to be a general trend shown on this chart.
Also, on the Hornady site Hornady
at the bottom of the page:
"To illustrate the effects of variations in bullet travel before the bullet enters the rifling, we'll compare a standard load with adjustments made only in the bullet's seating depth.
In a "normal" load with the bullet seated to allow about one 32nd of an inch gap (A) between the bullet and the initial contact with the rifling, pressure builds very smoothly and steadily even as the bullet takes the rifling. Pressure remains safe throughout the powder burning period (B), and the velocity obtained - 3500 fps - is "normal" for this load in this rifle.
Seating the bullet deeper to allow more travel before it takes the rifling, as in these next two illustrations, permits the bullet to get a good running start (C). Powder gases quickly have more room in which to expand without resistance, and their pressure thus never reaches the "normal" level. Nor does the velocity; with the same powder charge it only comes to 3400 fps (D).
When the bullet is seated to touch the rifling, as in the accompanying illustrations, it does not move when the pressure is low (E); and not having a good run at the rifling as did the other bullets, it takes greatly increased pressure to force it into the rifling. As the rapidly expanding gases now find less room than they should have at this time in their burning, the pressure rise under these conditions is both rapid and excessive (F). Velocity is high at 3650 fps - but at the expense of rather dangerous pressure.
Many rifles deliver their best groups when bullets are seated just touching the rifling. Seating bullets thus can be done quite safely if the reloader will reduce his charge by a few grains. The lighter load will still produce the "normal" velocity without excessive pressure.
This brings up another pointer on accuracy for shooters who may have a few thousand rounds through their rifle barrel and have noted a fall off in the accuracy they can obtain with their standard loads. Hot gases from the shots previously fired through the barrel erode the throat and thus increase the distance a bullet must travel before contacting the rifling. By loading longer bullets and seating them farther out so they'll touch the rifling - making powder charge adjustments as necessary, of course - accuracy can often be improved."
You may have to go to the site to view the pics.
I have experienced the same reduction in velocity when loading for a rifle that can not be loaded close to the lands due to magazine restrictions. The velocity is always lower. One time I seated one bullet with the same exact components and powder charge to get close to the lands instead of to fit the magazine and the velocity increased ~100 fps.