Set one of the monitors to use 125% DPI scaling. Start the attached project on a monitor with 100% DPI scaling - the form is expected to be with size 400,400. Move the form to the monitor with 125% DPI scaling. You are expecting the form's size to be 500,500, but it is 507,521. Please refer to the screenshots.

Workaround:

Override the RadForm.ScaleControl method as follows:

    Protected Overrides Sub ScaleControl(factor As SizeF, specified As BoundsSpecified)
        Dim initialSize As Size = Me.Size
        MyBase.ScaleControl(factor, specified)
        Me.Size = TelerikDpiHelper.ScaleSize(initialSize, factor)
    End Sub

Create a brand new project and add a ShapedForm. Please follow the steps illustrated in the attached gif file.

To reproduce:
public Form1()
{
    InitializeComponent();
  
    RadButton bt = new RadButton();
    bt.Dock = DockStyle.Right;
    bt.Parent = this;

    RadTitleBar tb = new RadTitleBar();
    tb.Dock = DockStyle.Top;
    tb.Parent = this;
    tb.Size = new Size(150, 100);

    this.Shape = new RoundRectShape(20);
    this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.Sizable;    
}