How to override gradle subproject config in module?

Question

My modularized Android project makes use of subprojects in the root build.gradle in order to minimize the configuration needed in each submodule's build.gradle. For example I can use it to add our custom buildType to each module

subprojects 
    afterEvaluate { project ->

        if (project.plugins.findPlugin('android') ?: project.plugins.findPlugin('android-library')) {
            android {
                buildTypes {
                    qa {
                        initWith debug
                        matchingFallbacks = ['debug']
                    }
                }
            }
        }
    }
} 

My assumption was that if I also added this build config to a module level build.gradle that it would override the project level defined configuration. However, this does not seem to be the case.

If I add the following to my app/build.gradle my app ends up with the suffix 'dev' when the QA buildType is selected.

buildTypes {
        debug {
            applicationIdSuffix = ".dev"
            signingConfig signingConfigs.debug
        }

        qa {
            initWith debug
            applicationIdSuffix = ".qa"
            matchingFallbacks = ['debug']
        }
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }

    }

The same problem also applies when I try to use buildType specific buildConfigFields in modules; they're ignored.

How do I get the module's buildType declaration to override that defined in the parent project? I read the gradle docs and it suggested a syntax like android.buildTypes.qa{...}, however this results in an error due to "method" qa not being recognised.