I would appreciate some feedback on how how small of a distance is reasonable on the head tube above the top tube and below the down tube? In the following drawing these distances are marked with blue circles and through the dark red dimensions: https://ibb.co/FsC1cKc

It's a titanium frame, 48mm OD head tube, zs44 headset.

Context: I want to maximize the space between the top tube and the down tube because I would like to put a hydration bladder there which wouldn't fit properly if the space is too small. On the other side I guess that welding too close to the bottom and the top of the head tube could warp the head tube where the headset bearings sit and thereby increase the probability for high-speed shimmy. This warping risk is what I thought is the limiting factor to making these distances smaller. True?
I am not welding the frame myself. A manufacturer will weld according to my specifications. I could just ask this manufacturer what is reasonable which I will do of course. But they may have an incentive to just say something with an unreasonably high margin of error (to guarantee no warping) because there is no downside for them to a high margin of error (i.e. they don't care about my water bladder goals) but a potentially large downside if they do mess up the head tube and have to throw away the tubes they have already welded together. Similarly: It will probably also be quicker and easier for them to manufacture the frame with larger distances above the top tube and below the down tube.

Have you tested out in practice what the (reasonable) limits (smallest distance) are here?