Welcome to the forum! The tires were a different width only in 1988 with the GT and Formula. All other years had the same size. The smaller tires on the front make it easier to steer at very low speeds.....like parallel parking.
Actually, all Fieros with 15" rims came with staggered tires from the factory....205/60/15 front, 215/60/15 rear. But in 86-87, the rim was the same front and back....in 88, they went to a staggered rim as well.
It is one of the basics of tuning. If your car is balanced 50/50, then you want the same size tires front and back to keep it balanced in the turns. If your car has 55% of the weight in the back, then you want 55% of your tread width to be in the back.
The 88's with the 15" laced wheels also had different offset front and rear. My experience with my 88 Formula.... Is don't run same offset wheel all around the car. It will make it rather twithcy at speed. Almost like the car is nervous. Make sure on the 88's to get the right offset wheel.