@KurtGodel7 said:
If Gibraltar's garrison is limited, that means it can't be defended against Allied attack.
To be clear, if you can have at most X land units in Gibraltar (which would need to be decided based on a guess of how many infantrymen is an infantry units and the broad assumption that the other land units take about the same space when deployed or in reserve but ready for immediate deployment), you can also attack Gibraltar with at most X land units. (No other rules for land units here.) This would make Gibraltar actually more defensible, possibly much more defensible.
(Obviously, this is an approximation: you should realistically be able to attack with infinite land units but only Y at the same time, with Y lower than X, then, when you win, every land unit exceeding X goes back to the transports (because it never left them), but I'm not proposing front-line based limits or anything else other than a max X both stacking and attacking for a few very small territories like Gibraltar and Midway. Ideally, every territory for which X would be greater than 10 gets infinite - so no limit - for simplicity (yes, an arbitrary upper limit over which not to bother): this would likely include Malta and every island bigger than Malta depending on how many men an infantry unit is representing.)
Moving on to air limits, Gibraltar would also have a maximum air unit limit to land (like an aircraft carrier) (again, arbitrary and limited only to a few extremely small territories like Midway etc.). In this case, however, there is no limit for attacking air units over Gibraltar. (Again, I'm not claiming this is very realistic.)
Practically, the land limit would favour the defenders and the air limit would favour the attackers.
In case of paratroopers, the limit would be total on land units. For example, if Gibraltar has a land unit limit of 2, you can offload 2 land units, or para-drop 2 land units or 1 of each, no more. (Again, a simplification.)
My point is not that this would be highly realistic, just that it would be more realistic than nothing, everything else being the same (and it is meant to be limited to Gibraltar, Midway and at most a few other similar cases if not just these two.).
Whether or not something like Gibraltar could be attacked with paratroopers at all is of course a disputable matter. Personally, I would say that a simple rule that Gibraltar can never be attacked with paratroopers unless completely undefended would be a good special rule to add for Gibraltar and anything else about as small as Gibraltar (as an approximation of how insanely borderline suicidal would such a thing be). An arguably more realistic rule would be limiting it to the unused stacking limit. For example, if Gibraltar has a limit of 2, then you cannot para-drop if there are 2 defenders, can paradrop at most 1 if there is 1 defender and can paradrop at most 2 if it is undefended by land units. In any case, the total attacking land units would never be more than 2.
