Yeah, that's what it has to be. My problem is I just don't like the terminology. When I read "higher.." I automatically think of "higher on the list" or "physically higher on the page/screen" rather than what Wrye actually means... "lower on the list but of larger numeric value".
-Decrepit-
Yep it did that to me aswell. Just remember the installer closest to the ==Last== marker will have its files in the game.
installer-1.7z
installer-2.7z
==Last==
Files from installer-2.7z will be in the game overwriting installer-1.7z files.
It works the same with sub-packages of an individual complex installer too.
10 Mod Core files (includes esp & some textures)
20 Mod Optional Hi-res textures <<-- Will overwrite Mod core files textures if this sub-package is selected.
What will really mess with your head is the first time you multi-select all installers to install at once - They will be installed in reverse order

and you watch thinking "OMG I cant stop it and I have the order upside down"...
It does this so there is one step less.....
Step 1: Installer-2.7z de-compressed and all files installed
Step 2: Installer-1.7z de-compressed and installed but skipping files which conflict with installer-2.7z (these skipped files are recorded as not-installed in case at a later date you un-install installer-2.7z)
If it did it in the order you think it should this would happen.....
Step 1: Installer-1.7z de-compressed and installed
Step 2: Installer-2.7z de-compressed and installed
Step 3: Installer-1.7z de-compressed and re-read to record files overwritten in step 2.
The process of installing multiple installers at once is quicker if done in reverse order.