Please refer to the attached screenshot.

To reproduce:

public RadForm1()
{
    InitializeComponent();
    
    Font f = new Font("Microsoft Sans Serif", 9.5f);
    this.radDropDownList1.DropDownStyle = Telerik.WinControls.RadDropDownStyle.DropDownList;
    this.radDropDownList1.Font = f;

    this.radDropDownList2.DropDownStyle = Telerik.WinControls.RadDropDownStyle.DropDown;
    this.radDropDownList2.Font = f;
}

Workaround:  If the text is not completely visible in RadDropDownList for a specific font you can increase the minimum height of the RadDropDownList and the DropDownListElement.TextBox.TextBoxItem.TextBoxControl.

public RadForm1()
{
    InitializeComponent();
    this.radDropDownList1.MinimumSize = new Size(0, 25);
    this.radDropDownList1.DropDownListElement.TextBox.TextBoxItem.TextBoxControl.MinimumSize = new Size(0, 25);
}