How many parts are typically in basket and how big are they (size and weight)? What type of machine are you using? Is it wheelblast or airblast? Describe how the basket is placed in the machine.
It's more about the volume of parts and the weight of the individual part. You don't want the tumbling action of the parts to impart more compressive stress into the part then the peening action itself.
What specification are you working to? AMS 2430 forbids tumble/batch peening.
What type of part are you planning on tumble peening? If it’s a spring or a stamping you are probably ok . If your planning on tumble peening a machined part I would advise that you don’t.