ScrollViewer scroll bar hard to drag by mouse if no margin

[GF-Huang]

Describe the bug

https://user-images.githubusercontent.com/4510984/166149377-997838bf-49a6-4e17-abd2-92ce87e23df5.mp4

Steps to reproduce the bug

See the video and reproduce by the demo.

ScrollViewerDemo.zip

Expected behavior

Easy drag no matter has margin.

Screenshots

No response

NuGet package version

HandyControls (Custom version) 3.3.11

IDE

Visual Studio 2022

Framework type

.Net 6.0

Windows version

May 2021 Update (19043)

Additional context

No response