Hi guys,
I am a new-ish user to foil kites and in desperate need of some help,

Issue: 2015 Flysurfer Sonic FR

When ever i sheet in the bar at all, the kite back stalls and looses all power. This issue wasn't as bad when i fully de-powered the kite - which shortens the center lines and respectively lengthens the real lines. (this suggests that my rear lines are too short, stalling the kite whenever i try and sheet in to gain more power)

To fix this issue, should i lengthen the rear lines - if so, by how much?

When my bar is fully sheeted out and depowered - the kite is fully powered. Any thing sheeted in or added power (lengthening center lines), the kite falls out the sky.

Please Help as i have missed many sessions because of this.

Thanks in advance guys.