You need to practice the tapering
methods spoken of here. Forests will have a disproportional amount of foliage at the top for the same reasons that forests do: no light or space below. We have to grow our forests from stock that is pretty close to the finished size of trees and mature them in-place, as opposed growing them in-place. This sounds like double-speak, but there are some absolutes that we have to deal with which are not different than a real forest: the internal branches will die over time. If you don't start with branches on the insides, you will never, ever grow any in there. A few will live that get some light, but most, -almost all will diminish over time.
Your tops are too big as a percentage of the foliage. You need to keep them smaller and pointy and essentially as a finished product as the lower limbs ramify and fill out the perimeter profile. Everything needs to be wired into flat layers and with plumb trunks. It never gets easier, and you will never have as many internal branches as you do now. Arrange them into finished intermingled positions (layers), almost without regard to anything (like which tree the branch is on) except filling in space where branches should be, and leaving space between layers where space defines layers. An observer can't really see that the branches don't grow from each tree in the fashion of a Christmas tree out in the open. Some trees will have almost no branches and the neighbors to the left and right will provide the alternating left-right-left-right layers, and that's OK. The observers look at the whole thing and if branches (layers) are flat (horizontal) and fill in all the space, or an appropriate amount of space, they assume the branching is proper and the whole will "look" right. Wire it now, it never gets easier. Make the top a series of pointy, individual tops and keep them tidy while the rest fills in. The tippy-tops do need to have a nice arrangement of tiny branches all in the right position and proportion, as a Christmas tree, because they are out in the open.
That will take you long enough to do for the rest of the branches to ramify and look good.