It's not so much a question of the height - it's about how far from the FD cage the chainring is, at the tail of the cage. If it's too far away, there may not be enough rigidity in the cage to get a clean small to big ring shift as it's the part of the mech "behind" the ring that initiates the shift.
Repeated pushing of the lever across with more force or enthusiasm that should be needed in order to "force" a shift might eventually cause lever failure (it is one cause that we know of) so it'd be important to get as clean a shift as can be managed.
So - if you use a non-Campag band on adaptor for your braze on mech, the majority allow a little radial motion of the FD in the location where the curved part at the front of the FD body actually fits - the part that corresponds to the braze on.
As you will be working quite a long way inboard (in effect you are moving the chanline "in" about 2 mm from where it would normally be), provided you can do it without the spring on the back of the FD fouling anything, you can try to mount the FD with the clip rotated "forwards" around the seat tube, so instead of having the "braze on" at the "6 o'clock" position (if you were to look at in in plan with the gear side lower-most), if you can move it towards the "5 o'clock" position, that will pull the FD forwards and in towards the frame slightly, so allowing (maybe) a better shift. The limit to how far you can take that game is the degree of rotation that the fitting allows (given that the cage of the FD needs to be parallel to the chainrings) and the bulk of the derailleur return spring - it depends on the seat tube size as to whether it will foul the seat tube when fully over to the left for the small-ring-to-large-sprocket combination or not. On 28.6 mm dia seat tube, you have quite a lot of room to play with, on a 35 mm dia seat tube, none at all.
I think an entry level, Veloce or similar, 10s FD, if you have one, would work better than an 11 and it will save you a bit of FD trimming - I'd probably be inclined to fit a chain catcher or given the ring sizes, maybe a dog-tooth as well. though. if you are keeping your 11s chain - the 10s cage is wider than the 11, so it doesn't work to control the chain on downshift quite as well.
Possibly needless to say, all the above is tried at your own risk - if your shift is lousy, you look down to see what's going on and end up under a bus, that's your call, not mine!
I saw the
@TheCyclingRooster set-up. I've done similar things for people but whether it works and how it works have a lot of contingencies. It'll work in some cases but not all and in some situations where it does work, it'll work better than in others. It's a lot easier to advise when you actually have the bike in front of you in the real world ... the Campag specs (just like SRAM, Shimano etc) are what they are because they have been real-world tested within the specifications given - apart from and beyond that, there are things that can be "made" to work but unless as a manufacturer you are going to start publishing a long and complex set of caveats, it's better just to say, "follow the spec and it will work & work safely, stray outside of it and dire things could happen". From a warranty point of view, where materials, workmanship and function are all being guaranteed, it's pretty much essential.
