Establishing time to achieve coverage (should be 98%, not 95%) and then using calculations for different parts is not only dangerous, it probably does not meet the requirements. You must demonstrate that you have achieved 98% coverage. From there you can do peening to "complete coverage" and in this case it would be just 98%. If you must do 150% coverage you would increase the exposure time by 50%. However, if you use a formula to calculate your exposure time for different size parts you may, or may not, have the correct (98% coverage). You should always perform trials to demonstrate you actually achieve the coverage required.
The coverage on the ID is another story. It will act a lot different then OD peeing due to ricochet (bouncing) media performing multiple impacts. You must also verify that you can achieve the required intensity within the ID.
I would not recommend that you rely upon formulas or calculations. Actual coverage inspection is always expected. You must be able to "Prove" you are correct with direct evidence.
