As mentioned previous, a Corsair with retracts folding straight back. Now add to that giant scale and maybe if you can afford them, Glennis wheels, beautifull but very heavy. You now have a situation where you could have a pound's worth of wheels and tires. And when retracted they move back, say, roughly five inches. So with a pound of wieght moveing back and forth like that, what do you do with CoG?

My guess would be balance with the gear up and use the rearmost point in the CoG range, because when you lower the gear you will move towards nose heavy.

If you balance with gear down in this case you risk being tail heavy with gear up.

Or spend some time checking and measuring where you are in both positions.