Huh?
Miami's deal is not better. Not remotely.
Valuing the additional year means you want more guaranteed money. 85/4 is more guaranteed money than 80/5. But I think since we're getting down to the nitty gritty, it's important to note that these values are first-year approximations, they're not counting raises.
Goran's true max contract over 4 years is 94.35 @ 7.5% raises and 90.9 at 4.5% raises, not 85M. The same can be said for Miami's offer, which would likely include the 7.5% raises as well, but the starting value difference of $5M+ plays into this.
Again, if Goran were S&T'd, the difference in value (including state tax differential) is $19.87M (given: MIA S&T'd to LAL) over 4 years. That's actually more money than the additional year Miami is offering. If Goran gets a 3+1 deal with a player option in year 4, he'd be 32 years old under a $108M cap looking for a 3 year extension in 16-20M range.
The 5 year deal at 80M is not good value for him.