The idea with the Symbols Along command is to set up symbols along the line you've drawn at equidistant intervals from one another (though this can be varied if required).

However, the Distance part of the command works from the symbol's origin point (that's where you'll see the cursor crosshairs meet when you pick up the symbol from the catalogue to first place it). This isn't always where you might expect it to be, and it may be that whatever symbols you're using are creating problems thanks to this facet. Without seeing exactly what you're trying to do, it's a bit tricky to advise more precisely than this.

The transparent space around the symbol is just that - emptiness. However, the amount of such space in and around the symbol may affect where precisely the origin point falls, so it can have an influence.

One possibility would be to set the Symbols Along line up with the symbols at or around that "too far" limit you mentioned, and then fill in the gaps with other symbols by-hand afterwards. You can always adjust the size of the symbols to fit whatever gaps there are, if they don't quite look right, or add some that aren't quite on the line to fill satisfactorily. More work, I know, but perhaps giving a better end result, especially if you want the palisade to look a little "lived in", where not every pole has been positioned perfectly, or cut from the same size tree.

It's fair to say that with commands like this, and also many of the Sheet Effects as a different example, it's often a question to trial and error - make a few tweaks, and then try again. You might want to set up a series of trial lines, and see which looks better, for instance. If you're like me, you might want to jot down exactly what you did each time though, so you don't forget what happened the one time it looked right ?

If you're still struggling, post an image or two here to highlight what's going wrong, and I'm sure someone will be able to assist you further.

Would it work better if the curled scrolls faced towards the viewer, instead of away? That's basically the way someone would read/view a scroll in many cases, so it may be that's what's making them look a little "off" just now.

Getting lighting to look right and yet still leave the map usable is a tricky balance from my limited experience. In an environment such as you've drawn so far, the lighting would be likely good and fairly uniform flat, or largely none at all, for each particular area, so it may be worth asking how many lighting effects you really need before embarking on setting it all up.

I think this may be what you need to see/read.

Sue's advice is excellent for adding your own clouds.

If you might be interested in using symbols instead - or as well as - you may like to see the Alyssa Faden style pack, which was part of the Cartographer's Annual in 2014, as that comes with a number of cloud symbols designed specifically for use on overland maps.