I have a sneaking suspicion that changing the position of a drive is an urban myth on modern drives. I have searched several times on this, and the only ref I can find are along the lines of your link, and couldn't find anything definitive from a drive manufacturer (didn't look very hard this time though). The nearest ting I came to definitive was
HERE which claims to quote manufacturers.
And in answer to your question, in my opinion, it doesn't matter a toss what position you put it in or when providing there is sufficient airflow/cooling.
Just try to orientate it with the PSU at the top if aesthetically satisfactory.
Bear in mind that a high proportion of NAS enclosures mount the drives vertically for better ventilation and heat dissipation, so there is nothing wrong in doing that.
Further searches produce these links. Here you go, from Seagate
HERE
And a 'second hand' quote from
HERE
Taken from Western Digital faq:
"Physical mounting of the drive:
WD drives will function normally whether they are mounted sideways or upside down (any X, Y, Z orientation). Of course, the physical design of your system may limit the positions in which the drive can be mounted. However, in all cases, you should mount the drive with all four screws for good grounding. Also ensure that there is enough air space around the drive for adequate air flow, and avoid mounting the drive near sources of excessive heat (such as some CPUs)."
