https://github.com/bitcoin/bitcoin/blob/5180a86c96bc05d2a731f70f36aae28ab5a3fad4/src/qt/sendcoinsdialog.cpp#L339

I think this is %1, not %2
{
    ui->customFee->setValue(GetRequiredFee(1000));
}
void SendCoinsDialog::updateFeeSectionControls()
{
    ui->confTargetSelector      ->setEnabled(ui->radioSmartFee->isChecked());
    ui->labelSmartFee           ->setEnabled(ui->radioSmartFee->isChecked());
    ui->labelSmartFee2          ->setEnabled(ui->radioSmartFee->isChecked());
    ui->labelSmartFee3          ->setEnabled(ui->radioSmartFee->isChecked());
    ui->labelFeeEstimation      ->setEnabled(ui->radioSmartFee->isChecked());
    ui->checkBoxMinimumFee      ->setEnabled(ui->radioCustomFee->isChecked());
    ui->labelMinFeeWarning      ->setEnabled(ui->radioCustomFee->isChecked());
    ui->labelCustomPerKilobyte  ->setEnabled(ui->radioCustomFee->isChecked() && !ui->checkBoxMinimumFee->isChecked());
    ui->customFee               ->setEnabled(ui->radioCustomFee->isChecked() && !ui->checkBoxMinimumFee->isChecked());
}
void SendCoinsDialog::updateFeeMinimizedLabel()