I don't know the strength of the family nor the intensity of the honey flow you're having, but I would say open it at least half way and see how they respond. Are they crowded and bumping into each other at the entrance? [Don't mistake the guard bees examination of the entering bees for "bumping".]
I just got this nuc last saturday. There are 10 frames in the hive and only 4 were in the nuc. so 6 were empty. Just foundation. I haven't looked in the hive since Saturday. I'm planning to look this saturday. The bees at the entrance were all crawling over each other. I thought it was just guard bees, but last evening was the first time I ever saw this.
I would make it larger but I wouldn't remove it altogether. A 4 frame nuc will have some growing to do and a large entrance (wide open) would be difficult for them to defend. Try a third open or maybe half open.
It's tempting to be a fancy beekeeper and use the good looking commercial entrance blocks, but just as effective are simple sticks of wood of your chosen length, that fit into the entrance. One stick will give you an entrance on the side, cut it in half and you can have your entrance in the middle (better for esthetics :lol.