I set gap as below:
<telerikChart:RadChart.DefaultSeriesDefinition>
                    <telerikCharting:AreaSeriesDefinition EmptyPointBehavior="Gap"
                                                          LegendDisplayMode="None"
                                                          ShowItemLabels="False"
                                                          ShowPointMarks="False">
On Y I set autorange:

 <telerikCharting:ChartArea.AxisY>
                                    <telerikCharting:AxisY ExtendDirection="smart"
                                                           MajorTicksVisibility="Collapsed"
                                                           MinorTicksVisibility="Collapsed"
                                                           PlotAreaAxisVisibility="Visible"
                                                           StripLinesVisibility="Collapsed" 
                                                           AutoRange="True"
                                                           IsZeroBased="False"
                                                           
                                                           />

My work require me to show empty data so that end of day say 5 pm is show on chart.
The Y are in 1000 range, when null data at 5 pm show - my chart look straight because the scale is too wide. Because Y axis always show zero.

So far I could not find solution, if i set autorange to fault, I find it too difficult to set step min/max etc.

What could be idea here?

Hello Joe,

I was not able to fully understand what is your question. I have attached a simple app to this response, it is based on your code and it works as expected. If you need further assistance I will ask that you try to explain again what you want to achieve, also please attach a snapshot of what you currently have and a drawing of some sort that depicts the results you are after.  

Regards,
Petar Marchev
the Telerik team