It is more realistic to move warships from one SZ to another.
But, would you retreat more than 1 TT to repair your Tank?
(Land movement are much slower and falling back damaged Tanks while staying in position with Art and Inf make such delay an issue. You also have to compare between planes for the cost. Aircraft mobility and versatility is way more interesting than 2 hits units which have to return to IC for repair.)
IMO, it is easier to consider that such unit are repaired right on place with spare parts.
A different procedure I suggested a while ago is that you can only repair one and have to pick a damaged Tank as casualty before allocating a hit to damage another Tank.
So, instead of 10 Tanks staying on battle until the 11th hits.
A second hits eliminates a first Tank.
This becomes far less effective, but it is easier to follow a single damaged Tank per stack.
However, I did not search on how to calculate such way of allocating damage.
