Question about the relationship between actual height and strength

I want to use the Inflate in Sculpt mode to achieve a function that select areas and adjust the strength and radius to make the model stand out a given height（such as 5mm)

I use Mask to choose the area and I can use Inflate to make the model stand out smoothly.However I cann‘t make the model stand out a given height。 What’s more If I adjust radius, althougt I click same place, the height is different

Could someone can help me to solve this problem or find a better way, thanks ~