It's true that "many people" may indeed like to start off slower but those data show clearly that for male initiated communication longer messages have increase

It's true that "many people" may indeed like to start off slower but those data show clearly that for male initiated communication longer messages have increased probability of reply. The recommendation for short messages is intended to maximize replies per unit time not the reply of any given message. I don't think there is a problem with either approach. Each strategy probably appeals to a different type of recipient. So the chosen strategy can be thought to partition the potential recipients into the different types. (If you send 'A' a long message and A replies A is of the type who likes long messages. 'A' very well might ignore all short messages. B might have the exact opposite preferences of A.) At this level of abstraction there's not a wrong answer to the question. By that I mean that the details and content of a message whether long or short are probably more important than the length for any given case. But if you're someone who prefers to act in an open, earnest manner it's probably best to go with that and partition out people who are mistrustful, cynical or otherwise turned-off by open, earnest action and communication styles. An analogous statement holds for those who prefer to act more closeted, subtle and aloof.