Determines how much of the picture (expressed in percentage of picture's height) will be used to reflect the picture displayed over the button surface.
The value of this property can range from 0 (no reflectivity applied) to a value of 100 (the picture will be reflected in its entire height). Lower or higher values will be automatically capped to the nearest valid value. The default value is 50.
Below you can see two buttons: the left one has a picture whose PictureReflectHeightPerc property is set to 20, the right one has a picture whose PictureReflectHeightPerc property is set to 100.
This property has no effect if the PictureReflectivityEnabled property is set to FALSE.
In order to perform changes to Pictures and Animations settings at Design-time take a look to the How to display bitmaps and animations section.