If you want items distributed in an area, so they are uniformly spaced, maybe you should create an area, use that for the initial distribution, so you get at least one of each item, in that area... Now draw another area, where you want at the size you want.. Then return to the initial area, select the Forest object, then using Item Editor, move all the items to want to the new area and put them exactly where you want them. I have found this workflow, very useful when I have a list of plants/trees I want to use, but I want them planted in specific positions. I just create a large enough area, to scatter all the items I need, then using item editor, I can extract one of each, deleting the rest. Then position, scale and rotate, as many of each item, wherever I want, around the scene, without having to draw or create areas for them and if I want to add more items, I can use the initial area to scatter that, then extract one using item editor and delete the rest.. While I find forest pack great for scattering grass, gravel over an area, it's not so good at garden design, when you want specific plants only in certain positions.. like neatly in a row along one edge of a plot and taller plants at the back and shorter ones at the front. Also point cloud makes it difficult to see what plant is what, so having an area to one side, where I can place one of each and even use text to label them, helps a lot.
Perhaps it may not help withr your specific problem, but it's how I work on many projects.