Well the list is long, what could be with bridled kites.
I don´t have any experience with 2 line kites, but can imagine they steer slower but with more power because you can´t steer with brakes (4 line traction/handle kites)/AoA differential (depower foils).
You steer only by altering the lift forces/bending the canopy.
There is though a lot of 2 liner kites you see on beaches that turn exeptionally well.
The towpoint is quite far forward and the canopy quite unsupported in the back at your kite, at least what I can see from the pictures, has to do something with it.
For my first steps in kite design a few years ago I read the Foilmaker manual for the software a couple of times, and it helps.
It is written though for 4 line handlekites mostly but most aspects transfer to modern depower foilkite design, not all of them.
There is an appendix called "symptoms and remedies" which cover the basic errors in most first diy designs.
If you want to design and make more modern kites, the rest can be found in this thread (mostly) at least what aspects matter/could play a role. How you design it in the end and which values work best for what size/design/concept is the true art of designing a well working kite. When you get a generally well working kite and thought you reached your goal, then comes the fine tuning giving it to a lot of riders getting their feedback, not only your own opinion. It´s the most fun part of the design I think how much you can learn from good riders. A lot of times the kite can be tweaked quite a lot with the bridle and mixer.
Pictures work up to a point.
It is important to make good pictures of the kite in air maybe with a drone even, compare it to the CAD data (canopy curve/twist/shape/billow/wrinkles/structure/profile shape), tell tales can help detecting flow seperation (on top sail mostly), but most important input from experienced (foilkite) riders.