it actually makes instant blitz easier.

if you invade on regular size, then the AI will have 1 unit up on you due to you having to attack and not getting the unit that pops out of the castle whereas the AI on defense gets the unit that got built that year to fight with.

if you invade on odd turns, the AI will only have half a unit out and hence you'll no longer be disadvantaged.

it usually doesn't matter much anyhow but it's worth a shot.