I think saying "bring your hips back to the bar" is confusing to a lot of beginning gymnasts. The main problem I see with BHC attempts is coming back to the bar first and then trying to drop back. I tell girls to drop back to a "candlestick" position on the other side of the bar. Also for beginning gymnasts I don't have a problem with a slight pike, as long as the drop back is straight enough. If the gymnast is piking down from the cast on that side of the bar, that probably implies the shoulders were halted over the bar which is the major obstacle to completing this skill. Most of L1-4s I work with don't have the strength to maintain a perfect hollow throughout this skill while attempting it though, and I'm okay with them piking at the hips a little towards the end if it helps them keep their hips closer to the bar and finish in front support. I make them push up hollow ASAP when they finish and work on the shaping otherwise, but I really want them to get comfortable with an aggressive drop back and coming right up to front support.