FHA / PMI - Sliding Percentage Scale?

[Sean Durham]

Hoping to find some clarity on this, I looked through several other topics but didn't see this specific question answered (Apologies if I've missed something.)

Is there a clear way to calculate PMI with an FHA loan on a property? I'm getting mixed messages between what our lender is giving us, usmortgagecalculator.com and several other resources. Do we have any leverage to negotiate this?

Is there a set rate/scale that lenders use based on LTV? Wondering if there's any advantage to shopping around, if lenders have different scales...

If it makes a difference, this is for a duplex we will be househacking / owner-occupy. 

As always, thanks for your wisdom.