Assuming your plants are getting the same culture, the main factor is Variety. Some varieties just bloom better and more readily than others. I'm assuming these are from rooted cuttings?

Another factor is a large enough pot. When these things get growing, they like a lot of root room. But you used the word 'planted' so I'm not sure if you have planted yours in the ground. If that's the case, they should have all the space they need and do well, as long as they have good drainage.

If you could post a photo, we might be able to notice if there is anything else that might be going on.

I agree with what you said about pots and roots Dave. I have grown Plumerias for 25 years. There is absolutely no question they grow better in the ground and do not really like their roots cooped up in hot pots. Sure they will survive but they never look like they do in the ground.

I had a Nassau that is tall and needs to be cut off next year. I decided I didn't really care and wanted to see just how much better it would do if I put it in the ground. Around the end of June I planted it. The growth, leaves was incredible.

Next spring, all of my big ones are going in the ground. I have some in the ground that are 10' tall and they are the picture of health. Never get droopy leaves, never sunburn even in heat and full sun. I sure can't say the same for the ones in pots. It's a constant effort.

Some say they don't mind crowded roots or small pots, I completely disagree. I don't think the roots like to be contained and even more so, they don't like to be hot.... Feet in the shade, heads in the sun.... and the only way to keep the heat off the roots is to put them in the ground..