Replied 8 September 2017, 12:30 pm EST
There is a chapter in the Developer's Guide titled Using Sheet Models. This information should be good information about how to program against the models. This is the intended use of .NET development, but we had some many customers moving from programming against COM objects, that this was completely different. So, we wrote wrapper classes (which you are using in the code snipets you have sent) that call into the object models to do things to the Spread. This would make processing of the code slower, since there is two or more calls being made for every line of code working with the Spread object. However, the code looks familiar to someone who is use to COM programming, which is why we created the wrapper class.
Take a look at our AgedReceivables sample as well. This shows programming using the wrapper class and against the models, so you can see first of all how to do this, but also it shows how much faster programming against the models the executable is.