There are two things that you need to do. First, you need to declare that this is a "task" entry. This is done in the form and view designer. Bring up your new task entry definition. Then, click on the task name in the designer. This will bring up a small menu on the right side. One of the items in the menu is "modify the properties of this entry" (or something like that). Select this and then set the "family" of this entry to be a "task". This should get it recognized and included in the summary.

The second thing you must do is to make sure your Priority, Status and Completion fields use the same "data names" for those fields and for the selections in the priority, status and completion elements. I'm pretty sure that the folder summary looks for these values by name. So, your names must match exactly. But other than those fields, you can add whatever you want.

Thanks Peter,

The first half I had already done; the second half I'll check but, does this mean I can't define a new view which looks for a different name and displays the same way?

For instance can I create a new Task Folder View  that instead of Status, it looks at Condition?

You cannot have the task folder look for any other items unless you use the built-in names. The task folder is not really extendable.