That's something I've noticed. When I start a building with a vertical beam, then add a couple horizontal beams, and then go to put that other vertical beam in from the top, if I have to extend it to get it to ground level, it doesn't work well. A hoe (the tool, not the mercenary female) is your friend when building things. Well worth the inventory slot.

Use the free placement key to attach a temporary vertical beam alongside your hanging support, then point your cursor at that and it'll snap neatly to the bottom. Snapping in general is all about having temporary scaffolds in the right places.

Originally posted by Sunny:

you have to be looking up to the contact point to attach it like you want

No, you don't. The place you're aiming just needs to be close enough to lock on.

Also always build on an east-west or north-south axis.

I came up with this one accidentally. I like to build my main framework and where I want a beam in the ground say on a low corner I discovered a short vertical beam would snap more easily and then the longer beam snaps over it in exactly the right place. I then shift the perspective to the short beam and deconstruct it. Or leave it if it’s not visible.
I absolutely hate the raise ground as I can never mine it smooth afterwards.

Build up 1 metre, then place a 2m piece downwards.
Or if you have stone, place 3 floor pieces in an L shape, and click a wood into the internal corner.

you have to be looking up to the contact point to attach it like you want, sit or dig or anything to be below it and be angled upwards

Lurksmore has right idea but seeing them sunk in fairly far, usually in draugr villages just means you will have problems replicating it for missing pieces. So in that case you run piece over from another side and then attach from bottom. You may have to sit your character down to see the bottom of beam. Convoluted but possible. When building you really only want all base pieces to be blue then work up, or may have to fill in with a bit of dirt. Sinking stuff in doesn't make it stronger. Luckily with draugr structures they don't go up high enough to make a floaty bit or two a problem. You can also start using reinforced metal beams to cheat a bit and sink them within regular beams. Many ways to skin the cat.

Sit down and look up at snap point.

To be fair object placement in Valheim is far better than in NoMansSky.

If you hold down shift it will temporarily turn of snapping so you can position it manually. (I think it was shift. I remapped it.)

my method for placing tricky build pieces is to have a temporary flat surface behind or under the target area. this gives the little cross hairs something to float on so you can place the piece either snap or custom.
a beam doesn't need to be IN the ground to grounded but if you want it for aesthetic reasons then this method work. I use it in virtually every build I do.

Start from the ground up. Your ground is too low if first item isn't blue. If I am understanding you correctly... Some times you just can't reverse engineer stuff. You can also fill in by raising the ground, not just flattening it. May or may not cause a bit of a hump which you can then correct later.

Use walls or floor tiles to create a snap point and after you place the beam remove the floor tiles or walls that you placed.

Originally posted by Foxglovez:

Start from the ground up. Your ground is too low if first item isn't blue. If I am understanding you correctly... Some times you just can't reverse engineer stuff. You can also fill in by raising the ground, not just flattening it. May or may not cause a bit of a hump which you can then correct later.

https://steamcommunity.com/sharedfiles/filedetails/?id=2977142832
I'm starting with existing structures so ground placement is stymied a bit. Sometimes I can just raise the ground but often that's not an option.

I keep seeing these abandoned structures with a beam set well into the ground.

Originally posted by Emelio Lizardo:

I keep seeing these abandoned structures with a beam set well into the ground.

Well, what you can do is for example:
1. place a floor piece 3m above the ground where you want to set a beam well in to the ground.
2. attach a 4m core-wood pole to the floor piece from below. It will snap to any of the four corners and be 1m in the ground.

In principle I don't know of any other (vanilla) way to do that.