UNR gives you a solid way to move through with no room to flail around, it basically lays out a path for you. The blue bullets are just as dense as on Normal.
The Normal version shoots only one sun wave which gives you much more room, making you hit Utsuho less and possibly go completely off direction.
I've timed out the Lunatic version, but never capped the Normal one.
"Flail around"? Well there's your problem. You have
more time to get out of the way of each sun on Normal, and you should still be moving to the same spots for misdirecting the suns. And by the way, you can learn where those spots are just by playing Normal (or Easy) - no Hard or Lunatic experience needed. The general approach shouldn't change across difficulties.
If you spend about the same amount of time moving from one spot to the other for each wave of suns, there's no net change in how much you hit Utsuho. It's a loss if you leave early, but you earn it back by getting back under Utsuho early. And unless you're going for a score run or something, there's no need to get aggressive by staying under her as much as possible.
The second set of suns is meant to restrict you, in more ways than one. Besides the less space you have, you're forced to stay roughly in place until the second sun comes out (for misdirection purposes). Thus you have less time to move left or right, and it certainly can mean the difference between getting by and getting walled. If Nuclear Fusion is harder, you're doing it wrong.
