When I'm writing a task 1 report, either for this blog or with my students, I never worry about 'grammatical range'. Here's why:
- First, how many different 'grammatical structures' can we really use in the space of only 8 or 9 sentences?
- Second, do we have time to think about including an example of a passive, a conditional, various types of clause etc.?
- Third, will these different structures be relevant? Will they work in the context of the description?
I think it's much more important to spend the 20 minutes thinking about how best to describe the information on the chart in a clear and logical way. In other words, I suggest that you focus on task response, coherence and accuracy. This is what examiners are really looking for in task 1.