Well then you both don't know what you are talking about.
It's 100% likely dealing with an old kite that B too needs to be lengthened. You do not fix something correctly that has shrunk by further shrinking (shortening) it. The fix you experienced by shortening B, is because it will partially correct the profile or mainly B engagement time, but the side effect is you have now reduced the AB limit and with that you have lost range the component parts being depower and lowend.
The primary bridle that experiences the most shrink of any bridle is Z. If you were to restretch one bridle it should be Z. You can restretch all the bridles and the kite will be close to level. Often though adjustments at the mixer or the kite bridles will last longer, or be easier to implement.
You can make a kite more stable by reducing B, but the bar(&trimmer) should be the way you do this. The kite designer has spent much effort finding the correct limit for B which is usually slack on modern kites, i.e. kites fly off A and not AandB at full depower. Reducing it will just impose arbitrary limits that are not needed.
How can you reduce B without reducing it? I.e. change the bridles so B engages more, but the AB limit stays the same or even increase the AB limit which is often needed but then reduce B in the profile by lengthening it?? Well simple you lengthen Z and C. Often though Z is only needed but C can be a help. Remember Z is 4x the length of B in the standard 421 mixer. So if you altered B 2cm and it fixed things, you would need to lengthen Z 8cm ( and C 4cm being 2x B) while keeping B the same. B does not stay the same when you alter a flysurfer mixer, which actually makes their mixers a bit annoying to adjust when fine tuning.
kitexpert wrote:
Kite can very well collapse no matter how loose Z is. Because main reason for front collapsing is too low AoA for the wing specifications, AoA or wing (airfoil) shape should be adjusted. Extending Z is a weird advice, there is a bit sense in it but not very much.
Yes AoA is what causes collapsing. Camber affects AoA. Z affects camber. Situation in foil kites exist where bar is pulled in but AoA is reduced.
kitexpert wrote:
Not all foil kites collapse, some of them ever not even once
I know how to do kite like that and it has nothing to do with loose Z.
All foil kites collapse. Wind can shift 90, even 180 degrees, kite can very easily find it's AoA temporarily negative, or itself way out of the window.
kitexpert wrote:For OP I suggest to stretch all A bridle lines
This is silly advice as A is rarely shrunk much. Z is the main problem he should stretch that, or just lengthen it. Ask any paraglider which bridle they always stretch, they will say the brakes (Z).