Adding to a plugin's options - woocommerce

Question

having bit of trouble adding an option to reduce stock on a product within a deposit plugin (woo commerce deposits). Currently the options as standard are: 'deposit' or 'full payment' - I wish to also add 'both deposit or full payment' so stock would be reduced if either deposit or full payment is taken.
Help, much appreciated!
Updated function#1:
public function payment_complete_reduce_order_stock($reduce, $order_id) {
$order = wc_get_order($order_id);
$status = $order->get_status();
$reduce_on = get_option('wc_deposits_reduce_stock', 'full');
if ($status === 'partially-paid' && $reduce_on === 'full') {
$reduce = false;
}
else if ($status !== 'partially-paid' && $reduce_on === 'deposit') {
$reduce = false;
} //added in...
else if ( $status == 'partially-paid' && $reduce_on === 'both'){ // added to allow reduction on both Deposit and Full
$reduce = true;
}
else if ($status == !'partially-paid' && $order->wc_deposits_remaining_paid == 'yes') { // Added to NOT reduce if prepayment taken then completing order
$reduce = false;
}
Updated function#2:
'deposits_stock' => array(
'name' => __('Reduce Stocks On', 'woocommerce-deposits'),
'type' => 'radio',
'desc' => __('Choose when to reduce stocks.', 'woocommerce-deposits'),
'id' => 'wc_deposits_reduce_stock',
'options' => array(
'deposit' => __('Deposit Payment', 'woocommerce-deposits'),
'full' => __('Full Payment', 'woocommerce-deposits'),
// added in...
'both' => __('Both Full Payment or Deposit', 'woocommerce-deposits')
),
'default' => 'full'
),
This is where I think I fall down:
Original 'Save all settings' function:
$reduce_stock = isset($_POST['wc_deposits_reduce_stock']) ?
($_POST['wc_deposits_reduce_stock'] === 'deposit' ? 'deposit' : 'full') : 'full';
I'm not sure how to add in the additional option, this doesn't work!:
$reduce_stock = isset($_POST['wc_deposits_reduce_stock']) ?
($_POST['wc_deposits_reduce_stock'] === 'deposit' ? 'deposit' : 'full' ? 'both' : 'full' ) : 'full';