Next time you are out practicing, or in a deserted area try this…
Ride along at about 25mph, lift your butt off the seat and lean back as far as you can and pull on your front brake, using your feet to hold your body back…notice the amount of dive your bike has…then try sitting normal on your bike at the same speed and lift your feet and pull on your fron brake, using your hands to hold your body back…
There should be a significant difference in the amount of front dive…putting weight on your foot pegs gives the bike more stability, similar to a cruiser…more weight on the seat makes the bike easier for direction changes…pendulum effect…that is what makes the sport bikes feel so…sporty and flickable…the “effective” CoG is changed, depending on weight centralization. This test will also work under accelleration…accellerate while leaning back, then accellerate with your chin on your bars…the bike will react differently for those situations as well.
You are correct that the CoG doesn’t change, or even gets worse if you stand up (because you will tend to have a more rigid grip on the bars and will weight the bars more), but if you just transfer the weight to the pegs and use your legs more, you will be pushing on the bottom of the bike lowering the CoG.
Engineers use this theory all the time when trying to perfect the handling of sports cars. That’s why a BMW drives so much better than a Mustang…they have a four link rear suspension that can be tuned to move the effictive CoG lower in the vehicle by changing the angles of the links…