Why is there extra spacing for some characters which cause QPainter::drawText to be cutoff?

Question

I'm trying to use QPainter::drawText() to render some Chinese characters. But in certain fonts, there is extra top spacing when drawing the text. Why is this happening to some characters only?

Tested on Qt version 6.6.3 & 5.15.2

Googled some info, but nothing really answers the question:

• Meaning of top, ascent, baseline, descent, bottom, and leading in Android's FontMetrics

• Qt Forum — Impossible to get true text hight with QFontMetrics/QFontMetricsF

• QTBUG-53271 — FontMetrics BoundingRect size is incorrect with chinese characters and any higher DPI text

As you can see below: green box is with metric height, while red is with bounding height. Sure, the bounding height does bound the entire text, but there is extra top and bottom spacing.

#include "mainwindow.h"
#include "ui_mainwindow.h"

#include <QPainter>
#include <QFont>
#include <QFontMetrics>

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::paintEvent(QPaintEvent* event)
{
    // Call base class implementation first
    QMainWindow::paintEvent(event);

    // Obtain the QPainter object
    QPainter paint(this);

    QFont font;
    font.fromString("Apple LiGothic");
    font.setPointSize(50);
    QFontMetrics metric(font);

    paint.setRenderHints(QPainter::TextAntialiasing | QPainter::Antialiasing, true);
    paint.setFont(font);
    paint.setPen(Qt::white);
    const int align = Qt::AlignLeft | Qt::AlignTop | Qt::TextWordWrap;

    QString text = "钳禾日当午";
    QRect bound = metric.boundingRect(text);
    bound = QRect(0, 0, bound.width(), bound.height());
    QRect metricBound(0, 0, bound.width(), metric.height());
    paint.translate(10, 100);
    paint.setPen(Qt::red);
    paint.drawRect(bound);
    paint.setPen(Qt::green);
    paint.drawRect(metricBound/*.adjusted(0,10,0,10)*/); // hack adjustment
    paint.setPen(Qt::white);
    paint.drawText(0, 0, bound.width(), bound.height(), align, text);

    text = "汗滴禾下土";
    bound = metric.boundingRect(text);
    bound = QRect(0, 0, bound.width(), bound.height());
    metricBound = QRect(0, 0, bound.width(), metric.height());
    paint.translate(0, 100);
    paint.setPen(Qt::red);
    paint.drawRect(bound);
    paint.setPen(Qt::green);
    paint.drawRect(metricBound);
    paint.setPen(Qt::white);
    paint.drawText(0, 0, bound.width(), bound.height(), align, text);
}