Grunt imagemin - watch multiple files/folders optimise single file?

Is it possible to watch multiple files/folders but optimise only a single file using grunt-contrib-imagemine and grunt-contrib-watch?

I tried like this: (part of gruntfile)

imagemin: {
  dist: {
    cwd: 'images/modules',
    files: ['images/modules/**/*.{png,jpg,gif}'],
    dest: 'images/modules'
  }
},

watch: {
   images: {
      files: ['images/modules/**/*.{png,jpg,gif}'],
      tasks: ['imagemin'],
      options: {
      spawn: false,
      }
    }
}

grunt.event.on('watch', function(action, filepath, target) {
  if (grunt.file.isMatch(grunt.config('watch.images.files'), filepath)) {
      grunt.config('imagemin.dist.src', [filepath]);
   }
});

But it doesn't work. It returns:

Running "imagemin:dist" (imagemin) task
Verifying property imagemin.dist exists in config...OK
Files: [no src] -> images/modules
Options: optimizationLevel=7, progressive, pngquant=false
Options: optimizationLevel=7, progressive, pngquant=false
Warning: path must be a string

Any ideas? Thank you.