IMO that's a waste of INTS. My advice is just to create a 'home defence' theater and, when on AI control, the AI will relocate the ints where needed. So i personally use 2x4 ints for that.
I agree, but it all depends on how you want to play. In all honesty when i play Germany idc if the UK strat bombs me all day long it makes no difference. between the IC i build and conquer, the small amount of strats they have and the regeneration of the attacked IC it has no impact on my efforts.
If i wanted to be truly cost effective and that was my primary concern, i wouldnt build any INTs and simply Sea Lion the UK straight out which simply removes the problem altogether. Doing so is so easy that it requires little preperation or effort.
I used to take my main Theater HQ rename it Berlin and put my INTs and Subs under its control, i still do so from time to time. However i find that the AI upon occasion will lump them all together or move them to a single airfield etc... typically it does ok, but i can do it more effectively with not much effort. I dont normally micro manage, so when i do this its usually one of those times.
When i use the 20 ints covering 10 IC depots its when i play a more historical approach in that i dont simply let the UK bomb the hell out of me without trying to defend myself. I tend to build a 200 base IC as Germany and as such end up with more good size IC depot/cities then other players which requires more INTs if i intend on making an effort to stop them.
In regards to the navy typically (depending on the nation) ill let the AI handle the existing units and ill use the newly built ones. For example ill make my self an invasion taskforce and keep it in port until i get all the ships i want for it, meanwhile i might let the Ai do what it will with most of the other units.