cyclone4 ibis models for OCT outputs wrong?

Hi to all.

I am using quartus prime 16.1.2 to generate the ibis model I / O to do the signal integrity.

I have a 3v LVTTL output line (fFPGA) that I have to be connected to an external chip.

In "pin planner" if I disable a series termination is generated a ibis model with 27.9 ohms output driver impedance

If i put series 25 ohm without calibration is generated a ibis model with with 11.7 ohms output driver impedance.

If i put series 50 ohm without calibration is generated a ibis model with with 11.7 ohms output driver impedance also.

where am I wrong?

I insert the simulations that confirm what I said:

BEst regards.