There are a number of articles which studied on the impeller design and its optimum location in the stirred tanks. If you read some of them, they may help you. I name some that I read and were really interesting:

1-Effect of impeller design on the flow pattern and mixing in stirred tanks (2006)

2-Impeller design for mixing of suspensions (2011)

3-Agitation energy efficiency in gas-solid-liquid stirred vessels operating at ultra-high solids concentrations (2016)

Dear Pouria

I really appreciate you.