Apparently there's a maximum screen aize for the VNC.

Admin workstation: MS Surface 8.1 Pro, 1920x1080 touchscreen, large fonts

Target: Dell laptop 8.1 Pro, 1920x1200, medium fonts

Symptom: Can’t scroll all the way to the bottom of the screen where the start button is. Also, can’t click anything using either finger taps or the pen.

If I use RDP, everything works including touch, and it resizes the screen appropriately.