Could Malta even capture something anywhere without concerns that the tail starts wagging the dog? Much less defend it from other countries without failing the previous 'rule'? (if in terms of islands the Italian Republics are very interested in stealing them).
Quite simply, while you might well be able to end up having an Empire which can trace its history back to Malta, prehaps even with it being a semi-sacred part of the empire, its all but impossible to have an empire based on Malta since somewhere else is ultimately better for centralizing the rule from (either due to better farmland support for the bureaucracy in said capital, closer contract to critical border holdings etc)