When you have appointments with different heights in the horizontal view and you set the MinAppointmentHeight on the ScheduleView to the minimun appointments height, appointments with bigger heights are set to the minimum one.
In facts when they are higher than the MinAppointmentHeight, they still have the proper height but are cropped by the MinAppointmentHeight. When they are lower, the MinAppointmentHeight generate a gap between the lower one and the next appointment.
You can check the bug here: http://www.telerik.com/community/forums/silverlight/scheduleview/minappointmentheight-for-different-appointments.aspx#2253898