i was watching my wahlbergii L1 as i was worried if they would be able to handle the d.hydei i gave them, and when i saw them catch one, they kind of just pinned it to the floor and began eating anywhere, it looked like the end of the thorax/beginning of abdomen (pretty much halfway). i dont think it had the capability to reposition it or start by eating the neck/head, the hydei is almost the same size as it. ive seen this also with older wahlbergii. they are known for attacking and eating prey their size or even bigger. when ive seen them do this, they havent gone for the head or neck i dont think, they just seem to start eating halfway between their forearms ie. directly in front of them, as the prey is so big.
however, watching my gongylus, whenever they catch a fly (very small compared to the gongs size), they never simply snap forward, grab, and snap back, there always seems to be (what LOOKS to me) as some repositioning. however this could be due to the fly struggling and the mantis trying to get a better grip on it too. but with gongs and flies, they always start eating the head or thorax, i have seen. maybe its because they can afford to, in terms of size of prey compared to their size and the size of their forearms. i think if a mantis were to attack another mantis of a similar size, itd be pretty difficult for it to go to all the trouble of repositioning, or reaching round to eat the head first, so they just eat whats there in front of them.
this is just what ive seen.