I almost forgot. Do Adenium rebloom from old flower 'socket '? After flower drop I usually pinch off socket.

You cannot relate the caudex size diameter or circumference as to whether the plant will flower.
At 1.5" - 2.5" you could see a bloom, but age of plant, amt.of sunlight and number of hours, vigor of the plant, nutritional requirements met. All play a part. When comes right down to it, they will bloom when they are ready.
I wish I could give you a definitive answer, but I do not believe there is.
Rick

No, they don't rebloom from socket, socket drop off after few days.

Marie