The instructions for the calibrator to define KFLDHBN are given in funktionsrahmen module LDRLMS 3.1000. Reviewing my translation doesn't make it abundantly clear what is done, other than making reference to the turbocharger compressor map as you say:

"KFLDHBN: Firstly, in the compressor performance map, acquire the regular full load line at the speed sample points of KFLDHBN as well as the maximum pressure ratio line (due to the surge limit, maximum turbocharger-speed or prohibited areas of poor efficiency) to define the operational limit.
Then continue on the altitude gradients from the normal full load line starting at any engine speed, up to an operating limit.
The volumetric flow rate increases with increasing altitude (decreasing ambient pressure) and the pressure ratio with 1013/ambient pressure.
This new intersection then defines the maximum pressure ratio for KFLDHBN at the respective engine speed."

My understanding is that this map is to limit turbocharger performance at higher intake air temperatures and altitude when the charge density will be lower.

Sorry that this probably doesn't help you much. I don't know whether tuners fiddle much with this map. Looking at the BAM file, there isn't much difference in the ratio until you start getting above 70°C IAT. I don't think it's worth too much thought for UK temperatures and altitudes.

TTQS

Critical part on this one is turbo speed and compressor outlet temperature (because for example some connection hoses can't handle more heat permanently). All cars that are used to create the calibration have turbo speed and temperature sensors and are driven under various conditions to find the PR that keeps thinks into these defined limits. This is the intention for the function. You have to make it fit your needs on a modified vehicle (I ignore the temperature thing and just use the compressor map to make a safety net for overspeeding).

If it helps here is the stock KLFDHBH from my Original tune and also the KLFDHBN from the hybrid I have been running. Its a 2283 compressor wheel so obviously capable of far more than the stock wheel. I'm thinking its just one of those maps that's either correct or not and not something that needs tweaking, It would be helpfuly though If there was someway of working out how these figures where gotten to as I have a 2280 series wheel that I would like to map and just want to make sure that the map is correct.

Yes.

To calibrate it properly you have to either equipe your turbocharger with a speed sensor and drive up the mountains or simply take the compressor map, do some calculations and enter the values to have a good guess.

i used to have this maxed out.  however i put on the rs4 table attached here.  i boost 23-24 psi on occasion with k04's, although right now i have a parallel mbc pegged at 20psi for some fuel fine-tuning.  this table has never bothered me nor got in the way since switching to the rs4 map intended for k04's written correctly onto the s4-axis table in the s4 m-box.

stage 0 - 2, stick to stock M-box or M-box multiplied.
stage 3, stick to the table i uploaded.
stage 3+, like nyet/nvr said, not functional.

So just to revive this old topic because i've been trying to dial KFLDHBN in I wonder why shouldn't I just use the exact same KFLDHBN from the RS4 including the rpm and temperature axis (which is different as well)?
Also I've managed to take a peek into a RS4 MTM stage 1 file and it seems they have modified KFLDHBN a bit to allow elevated boost as well.

The difference is shown here: http://nerd.hu/kfldhbn.txt

So I wonder what are you guys have been experimenting with in the past couple of months?

Thanks