Oncidium growth habit

[Dumb chemist]

I have a number of Oncidiums. My Onc leuchochilum and ornithoryhchum (excuse my spellings) show normal (?) growth with pbs coming from a central place slowly moving out from the center as new pbs are added each year.

On the other hand, I have Onc's. "Gower Ramsey" and "Sweet Sugar" that show a vertical growth habit. That is, a pb is at the surface of the bark mix. The next bulb is growing about a half inch above the bark mix off the first bulb. The next bulb is off the half inch high bulb by about a half inch making it an inch above the bark mix, and so on and so on.

Am I doing something wrong with these 2 Onc's to cause this growth behavior? Both Gowers and Sweets are growing in terra cotta pots using a standard orchid bark mix. Is attaching them to cork bark slabs considered better?