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

I think this is %1, not %2
connect(ui->groupFee, SIGNAL(buttonClicked(int)), this, SLOT(updateFeeSectionControls()));
        connect(ui->groupFee, SIGNAL(buttonClicked(int)), this, SLOT(coinControlUpdateLabels()));
        connect(ui->customFee, SIGNAL(valueChanged()), this, SLOT(coinControlUpdateLabels()));
        connect(ui->checkBoxMinimumFee, SIGNAL(stateChanged(int)), this, SLOT(setMinimumFee()));
        connect(ui->checkBoxMinimumFee, SIGNAL(stateChanged(int)), this, SLOT(updateFeeSectionControls()));
        connect(ui->checkBoxMinimumFee, SIGNAL(stateChanged(int)), this, SLOT(coinControlUpdateLabels()));
        connect(ui->optInRBF, SIGNAL(stateChanged(int)), this, SLOT(updateSmartFeeLabel()));
        connect(ui->optInRBF, SIGNAL(stateChanged(int)), this, SLOT(coinControlUpdateLabels()));
        ui->customFee->setSingleStep(GetRequiredFee(1000));
        updateFeeSectionControls();
        updateMinFeeLabel();
        updateSmartFeeLabel();
        
        ui->optInRBF->setCheckState(Qt::Checked);
        
        QSettings settings;
        if (settings.value("nSmartFeeSliderPosition").toInt() != 0) {
            
            
            int nConfirmTarget = 25 - settings.value("nSmartFeeSliderPosition").toInt(); 
            settings.setValue("nConfTarget", nConfirmTarget);
            settings.remove("nSmartFeeSliderPosition");
        }
        if (settings.value("nConfTarget").toInt() == 0)
            ui->confTargetSelector->setCurrentIndex(getIndexForConfTarget(model->getDefaultConfirmTarget()));
        else
            ui->confTargetSelector->setCurrentIndex(getIndexForConfTarget(settings.value("nConfTarget").toInt()));
    }
}
SendCoinsDialog::~SendCoinsDialog()