I know KFLBTS is activated with respect to the EGT model but why so lean just ahead of what I'm seeing is boost onset?

EGT's are already high if this map is active so what's the deal? I've seen this before on other ME7.x versions with other manufacturers but never really understood why?
After the initial lean section it get's properly rich as you would expect a lambda protection map to....

Attached screen shot is from ME7.5 Jetta 1.8L 180hp stock file.

Thanks in advance for any input

I suppose that makes sense, but then why have it default so lean?  Some factory KFLBTS maps I've seen were all lambda 1 in those areas and did not trend lean like the image I attached.

Additionally I've seen tune files from medium sized tuning houses like BC consulting actually increase the lean bump in certain areas... feel like there's something I'm missing 

Pretty sure, I have the damos for it and I've seen more than a few stock maps this way including the professionally tuned files I've seen.

It's also reflected going back as far as Motronic V3 as you can see the main fueling maps do the same thing (to lesser degree) just before boost onset and the enrichment of the mixture.  Initially I though it might be to help put some heat into the exhaust for catalyst warm up or turbo spooling but that just doesn't add up, especially when you consider KFLBTS is only used when EGT model activates it.

Lamfa on these maps is at 1.0 across the board except at low load, high rpm which makes sense. Maybe I just need to read more 

He has the damos he said

By one byte exactly.