What kinds of changes can I attempt on my object detector .config file to improve the detection accuracy?

I have trained an object detection model with 2 classes, around 7500 images, and approx. 10,000 annotations per class. I was able to fine-tune Faster R-CNN with ResNet (V1) from the Tensorflow Object Detection API. As you can see from the green boxes, it was successful in detecting these plants that it had never seen before. However, there are still several other plants that it needs to detect (as shown by the drawn-in red boxes).

Assuming my training data has sufficient samples to train with (it does), what kinds of changes can I make to my .config file to get more accurate detection results?

Here is my .config file showing the training parameters that were used:

# Faster R-CNN with Resnet-50 (v1)
# Trained on COCO, initialized from Imagenet classification checkpoint

# This config is TPU compatible.

model {
  faster_rcnn {
    num_classes: 2
    image_resizer {
      fixed_shape_resizer {
        width: 1024
        height: 1024
      }
    }
    feature_extractor {
      type: 'faster_rcnn_resnet50_keras'
      batch_norm_trainable: true
    }
    first_stage_anchor_generator {
      grid_anchor_generator {
        scales: [0.25, 0.5, 1.0, 2.0]
        aspect_ratios: [0.5, 1.0, 2.0]
        height_stride: 16
        width_stride: 16
      }
    }
    first_stage_box_predictor_conv_hyperparams {
      op: CONV
      regularizer {
        l2_regularizer {
          weight: 0.0
        }
      }
      initializer {
        truncated_normal_initializer {
          stddev: 0.01
        }
      }
    }
    first_stage_nms_score_threshold: 0.0
    first_stage_nms_iou_threshold: 0.7
    first_stage_max_proposals: 300
    first_stage_localization_loss_weight: 2.0
    first_stage_objectness_loss_weight: 1.0
    initial_crop_size: 14
    maxpool_kernel_size: 2
    maxpool_stride: 2
    second_stage_box_predictor {
      mask_rcnn_box_predictor {
        use_dropout: false
        dropout_keep_probability: 1.0
        fc_hyperparams {
          op: FC
          regularizer {
            l2_regularizer {
              weight: 0.0
            }
          }
          initializer {
            variance_scaling_initializer {
              factor: 1.0
              uniform: true
              mode: FAN_AVG
            }
          }
        }
        share_box_across_classes: true
      }
    }
    second_stage_post_processing {
      batch_non_max_suppression {
        score_threshold: 0.0
        iou_threshold: 0.6
        max_detections_per_class: 100
        max_total_detections: 300
      }
      score_converter: SOFTMAX
    }
    second_stage_localization_loss_weight: 2.0
    second_stage_classification_loss_weight: 1.0
    use_static_shapes: true
    use_matmul_crop_and_resize: true
    clip_anchors_to_image: true
    use_static_balanced_label_sampler: true
    use_matmul_gather_in_matcher: true
  }
}

train_config: {
  batch_size: 2
  sync_replicas: true
  startup_delay_steps: 0
  replicas_to_aggregate: 8
  num_steps: 100000
  optimizer {
    momentum_optimizer: {
      learning_rate: {
        cosine_decay_learning_rate {
          learning_rate_base: .0001
          total_steps: 100000
          warmup_learning_rate: .000033
          warmup_steps: 2000
        }
      }
      momentum_optimizer_value: 0.9
    }
    use_moving_average: false
  }
  fine_tune_checkpoint_version: V2
  fine_tune_checkpoint: training/faster_rcnn_resnet50_v1_1024x1024_coco17_tpu-8/checkpoint/ckpt-0
  fine_tune_checkpoint_type: detection
  data_augmentation_options {
    random_horizontal_flip {
    }
  }

  data_augmentation_options {
    random_adjust_hue {
    }
  }

  data_augmentation_options {
    random_adjust_contrast {
    }
  }

  data_augmentation_options {
    random_adjust_saturation {
    }
  }

  data_augmentation_options {
     random_square_crop_by_scale {
      scale_min: 0.6
      scale_max: 1.3
    }
  }
  max_number_of_boxes: 100
  unpad_groundtruth_tensors: false
  use_bfloat16: true  # works only on TPUs
}
train_input_reader: {
  label_map_path: training/faster_rcnn_resnet50_v1_1024x1024_coco17_tpu-8/label_map.pbtxt
  tf_record_input_reader {
    input_path: train.record
  }
}

eval_config: {
  metrics_set: coco_detection_metrics
  use_moving_averages: false
  batch_size: 1;
}

eval_input_reader: {
  label_map_path: training/faster_rcnn_resnet50_v1_1024x1024_coco17_tpu-8/label_map.pbtxt
  shuffle: false
  num_epochs: 1
  tf_record_input_reader {
    input_path: test.record
  }
}