First things are not 100% final, but I am as said very happy so far, I do need to test more. I don't have measurements, but can take them later. My measurements for the 18m most likely will not translate directly to the 9m. There is a formula for bridle size conversion, I will have to look for it unless someone else can share it. It is not always exactly correct in the figures it produces. This is most likely because the setup for different sizes needs to be slightly different. What I can do now is share how I did the mod, so you can replicate it on your 9m.
First you will want some measurements. You'll need 2 screw drivers and a measuring tape.
With the kite laid out on some grass, fix both front mains together with a screwdriver in the ground. Now I measured all full depowered endpoints for B C and Z and A main and pulley lines, everything there on the mixer. What is only needed for this mod is the difference between A and B, or the AB limit. I have the numbers for mine which "may be similar" to yours. My AB limit was 544mm. This measurement is wrong from new as my mixer has already shrunk. But it is still working, as B is still going slack at the edge of the window, which was the behavior at new. The negative to this being shorter is obviously less depower, but the kite won't fly forward as easy in light winds particularly from the center window.
Next I fixed separately both front and rear mains so both A and Z mains are equal at the top. A mixer test. I measured both C and B difference from AZ. You only need B, my measurement was B +105mm.
First you will need about 2-3meters of kite line and something to cut it before proceeding.
Lay out one mixer so you can start disassembling it without getting confused where the lines all go. Use nice big bit of space to do this. Keep the other mixer untouched so you can reference it for how things joined up before.
Disassemble the front and rear mains from pulley lines and AZ mains and front and rear lines. Always try preserve the open layout of the mixer while things are disconnected so you can easily reassemble without crossing or TWISTING things!
Remove the C pulley line completely, it's gone
Remove the B Pulley line and attach it to the front side of the B pulley.
Remove the C pulley, make a small 2-3inch kite line loop that goes the C pulley and has a 8 knot on the end.
Remove the A Main from the A bridles, double it over and reconnect the sewn ends to the A bridles. Make a 20cm kite line loop with 8 knot A main extension. Larkshead the A main double loop end under the 8 knot.
Assemble the Amain extension , C pulley loop and front main. Make a 50cm kite line loop with 8 knot front line extension. Larkshead the front line to above the knot. Attach frontline extension to front main. The mixer is now coming together!
Thread the B Pulley line through from the top of the C pulley and then through the front of the B Pulley. Be carefully not to twist it at all.
Make an overhand knot on the stitched section of the B pulley line loose end. Do this away from the Loop.
Make an 8 knot on the Z main 40cm up from the loose end. Larkshead the Z main loose end back onto itself above the knot. This is a little tricky if you have never done it before. This forms an adjustable loop on the Z main bottom.
Attach the rear main to the B pulley line. Move the over hand knot to be hard or close against the rear main but dont use the rear main as part of it.
Make a 8 knot in the middle of the rear main. Larkshead the bottom of the Z adjustment loop to the bottom of that knot.
Reconnect the rear line to rear main. The mixer is now fully connected and only needs to be adjusted.
Adjust the C pulley loop to about an inch or smaller.
Screw driver the front mains. Adjusted the A main length till the AB limit is the same as before.
Do a mixer test and adjust the Z adjustment loop till B is the same as before. When adjusting these loops you will need to be careful to balance them before tightening the larksheads.
When making the loops for the first mixer, if you cut for the second it will go much faster!
Repeat everything for the second mixer. You should be able to just copy the lengths off the first, Infact things like the C Pulley loop and A mains should be copied, UNLESS there is symmetry problems, which you can now fix with all the adjustments you have!
Remove ALL THE C BRIDLES.
Move the 2 tip B bridles, to the C attachments, 2 loops around the attachment LCL on the outer then 1 to the inner.
Fly the kite, adjust the trim at the bar, then at the front line adjustment.
Test and have play with things. You have a easy adjustment for Z, move the larks head to the Zmain, B pulley line join to lengthen and get more stability, better upwind. Move it down to the Front line front main join to shorten and get more power. If you want to adjust it further, adjust the loop on the Z main. The mixer test on the A15 doesn't seem to translate quite right when the mixer changes like this. The camber increase is less on this mixer and most likely the mixer test on the A15 does not measure at the correct sheeting point. You will need to play with Z to get exactly what you want. I highly suggest trying the 3 settings for different conditions so you can get a feel for their advantages and disadvantages.
Good luck and don't hesitate to ask me to explain more for you. If you are confused about something I write ask me!