And as manually halted the other 8 should be manually removed as well, why if I don't want download them should I wait the end of download to be able to remove them using that system ?
So you can change your mind on wather you want the other or not, so that you can at any time halt or resume the sub files, and once you decided you have enough you can cleanup all unfinished stuff keeping finished files.
Its how any half decent torrent client handles the issue and I see no good reason to change that to something else.
Overhead will be ignorer.
As i explained in the previous post you can not get the packet lost stats and those i see no way to improve the estimation further.