Modifying ADDON_SOURCES in addons_config.mk

I'm having some trouble compiling my fork of ofxOpenNI (experimental branch, using OpenNI2 + Nite2) with the makefile system. For some reason any app I make that tries to include ofxOpenNI (by including it in addons.mk) can't find ofxOpenNI's src/ directory. E.g: make inside of the project errors with:

ofxOpenNI.h: No such file or directory
 #include "ofxOpenNI.h"

It seems like the simple fix would be to edit ADDON_SOURCES in ofxOpenNI's addons_config.mk file to explicitly include it's src/ directory, but any of the following examples haven't seemed to work:

ADDON_SOURCES = ../src
--or--
ADDON_SOURCES = ../src/specific_file.h
--or--
ADDON_SOURCES = ../../../addons/ofxOpenNI/src/specific_fil.h

In all instances my app, in apps/myApps/OpenNI/ can't find addons/ofxOpenNI/src/ files.