Mega backdoor Roth in plan conversion

Hi,

 

I have some pretax dollars in ROLLOVER IRA (that are invested in ETFs)

But I would also like to maximize my backdoor Roth option. To do this, I have post tax dollars deposited in my 401k that are then converted to Roth dollars by doing an in plan conversion. 
Then I get this amount converted to a Roth IRA (where I again invest it in ETFs)

 

In this case will the amount that I am converting to ROTH IRA be subjected to the PRO RATA rule since I have pre tax roll over IRA dollars ? 
Fidelity advisers are unsure since I am doing an in plan Roth conversion