Taxi, those white lines indicate where the model's frame node is. If the frame is above the bsp, the object will spawn. If it is below the bsp, no matter where the rest of the model is, the object will not spawn. Swordedit already adjusts a model around its frame and the lines I thought were already shown in some previous version of swordedit. I don't see them now though.
Samuco, you would select something, click once to snap its bounding box to the sbsp ground, and click twice to snap its frame to the sbsp ground. That would be the best way, probably.
Also, check out this hex code in your hex editor. It's the sbsp code from Guerilla, which probably has not been reverse-engineered since kornmann00 enabled some fields. I did discover how to increase the limits of chunks and change the allowed tag types for dependencies in chunks, but this would probably just break Halo unless it was done such so that it would "expand" the modding wiggle-room for dependency types. Anyway, this is more for the HaloMods community.
The whole thing is in little endian. The tag class comes at the end, then you can skip back to the top and ... well, it's typically somewhat scrambled in the order that it is presented. You mostly see pointers (generating random memory addresses or offsets is common in the HEK tools). Sometimes you have maximum chunk counts.
If you mess with the chunk counts, that's fine but will probably break the engine when it is played.
If you mess with the pointers, you might get an error like this:
EXCEPTION halt in \halopc\haloce\source\cseries\debug_memory.c,#165: Attempted an operation with pointer at 0x73627370, outside of the valid pointer range. (\halopc\haloce\source\tag_files\tag_groups.c:2802)
If you add a weird tag type, you might get an error like this:
EXCEPTION halt in \halopc\haloce\source\tag_files\tag_groups.c,#308: group->child_count==0
If you change the block sizes found next to the maximum block counts (the block sizes are like 20-48 in decimal value and the block counts are typically byte-size numbers like 4, 8, 16, 64, 128, 512 and 1024, although they can be seemingly arbitrary limits like 200 or 800), then you might get an error like this:
EXCEPTION halt in \halopc\haloce\source\memory\byte_swapping.c,#88: object_attachment_block bs data @0012DDAC is #72 but should be #80 bytes
Either you are groping for answers, or you are asking God and listening to Jesus.