if you lower the resolution of the game window (playing in windowed mode and resizing the game window), the mouse sensitivity will increase, making it so you need to change the in-game sensitivity every time you change the resolution (game window)
Linked issues
duplicates 1
Comments 2
Thank you for your report!
However, this issue has been closed as a Duplicate of MCPE-22136.
Please add a vote and any new information to the main ticket, which will be updated accordingly.
If you have not, you might like to make use of the search feature before making a new ticket, as it's likely that the issue has been reported already.
Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Feedback – 📖 Game Wiki
It could be because the game adjusts to the small area for camera movement.