Setting the paper size for QPrinter to a custom size has no effect on the final printed page size

#include <QApplication>
#include <QPrinter>
#include <QPrintDialog>
#include <QPainter>
#include <QDebug>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QPrinter p;
    p.setPaperSize(QSizeF(5, 5), QPrinter::Inch);
    QPainter pp(&p);
    pp.drawRect(p.pageRect());

    QPrintDialog d(&p);
    qDebug() << p.printerName() << p.paperSize() << p.paperSize(QPrinter::Inch) << p.paperRect() << p.pageRect();
    if (d.exec()) {
        qDebug() << p.printerName() << p.paperSize() << p.paperSize(QPrinter::Inch) << p.paperRect() << p.pageRect();
        
    }
    return a.exec();
}