i think i may have sussed why some people have observed them targeting the head area. The mantis presumably has sensors on its legs that can tell when the prey is not gripped properly, ie when the bigger part of it is flapping around and not properly secured. It would just have to compare signals from each leg to know the direction of this movement. The motion thus analized, if too large, simply stimulates a change of grip to grap the part that's moving too much, which of course will likely be the thorax/head end rather than the abdomen. It may then start feeding there.
This may explain why it may APPEAR like the mantis can recognise the head end by it BEING the head end and not simply it being the part struggling most. In large dangerous victims, when the mantis is likely to start off grabbing hold with both legs of one half or the other, if it grips the abdomen end first it may need to shift its grip to the front later. On small victims, its original grip will most likely control its whole body, so there is no loose part that needs to be 'captured', hence the observations that they start feeding anywhere in some instances.
sorry if ive duplicated anyones idea, i have not gone through every post yet. cheers
