It's true that the leaf span is the real indicator of maturity, rather than the height. A good way to know when to expect blooms from a previously bloomed Vanda of any size is this: if it blooms regardless of the time of year, just note how many leaves are above the emerging spike to determine when it will potentially spike again. If you have a Vanda that blooms below the fourth from the top leaf, then once you get one mature leaf you have 3 more leaves to go before it will potentially spike. If I had to make a generalization for vandaceous hybrids, I would say 4 or more mature leaves on both sides should be large enough to bloom. Does that make sense?