inner clearance doesn't matter so long as the wheel doesn't hit the strut. outer clearance is what hits the fender on the big bumps.
offset is that its the distance of the midpoint of the wheel width to the hub surface, hence why it changes with width.
so if you want a quick way to visualize offset on the two wheels (given they're the same offset), ust picture the wheels 1/4" wider on the inside and 1/4" wider on the outside. there's no problem with adding 1/4" more width on a stock wheel. its just like going from 205 tires to 215 tires.