ASHRAE 90.1-2007 article G3.1.1 exception (a)

Hi everyone, I have a question regarding the reference's HVAC heating energy source for my projet. Here's the general outline: My project consist of an office building with 3 above-grade and 1 below-grade levels, plus an underground parking lot. The building's floor area is 88 000 ft2 and the parking lot is 47 000 ft2, for a total of 135 000 ft2. The proposed building heating source is all electric, while the parking lot's heating source is natural gas. My understanding of G3.1.1(a) is that I can use a different HVAC system type for the parking lot, since its heating source is different from the rest of the building and its floor area is greater than 20 000 ft2. Following this, I would use a system type 6 for the building and a system type 5 for the parking lot. Could someone confirm if my methodology is correct? Thank you.