Operating system: Any
Graphics card: Not related
Broken: 2.80, any
Short description of error
Grease Pencil Point property "pressure" has max. value 1. This applies when accessing from python. With Sculpt Mode, you can get much larger values.
If it's acceptable solution, it should be enough to increase the max value in the function rna_def_gpencil_stroke_point, file source/blender/makesrna/intern/rna_gpencil.c.
Exact steps for others to reproduce the error
Draw simple Grease Pencil line.
Switch to Sculpt Mode.
Select Thickness brush.
Make the line thick.
Switch to Scripting and run this code:
point = bpy.data.grease_pencils.layers.frames.strokes.points print(point.pressure) # prints for example 15.351 point.pressure = 10 print(point.pressure) # prints 1, you can also see the change in the 3d view; if my fix is applied, this line prints 10.0