How big are pull ratios in Shimano 9-speed front derailleurs in MTB and road bikes? I am asking about 3x9-speed front derailleurs.

The background this time is longer than the question -- I have a Sora based gravel bike and now I try to marry road shifter with MTB front derailleur with almost a success:

front , rear

small + big = works 
small + small = works
middle + big = works
middle + small = works
big + big = works
big + small = does NOT work


It means I cannot push cage outwards enough. It is all about some shy 1.5 mm, I cannot believe I am so close to success and yet I see failure. It is not high limit screw on the derailleur, I am simply out of cable pull to shift the cage just a hair further.

So I wonder, what are those cable ratios, are they so minuscule different then they manifest in ~1.5mm of shortage pull? Or could it be that I have to use the same group for the derailleur and crankset (currently I have Alivio and Acera accordingly; for tests I tried not to spend too much money) because such behaviour is not caused by cable pull ratio difference?
I've had something like this on two road bikes - the big-front and small-rear combo means the chain is running as far to the right as possible as it hits the front derailleur.

One was fixed by using proper-sized 9 speed chain, not the mystery chain that was already installed.

Since the limit screw is not the problem, you may need to shim the derailleur so the whole thing stands to the right a tiny bit more.  If its a braze-on mount this won't help.

Do test if you can move the cage far enough with your fingers (be careful!)

Another possible fix might be to distort the front mech's cage, but that may cause problems with other gears.