I’ve never tested it but unless I’m geared out there’s little chance that I could put out more power standing than sitting for intervals more than about a minute.
Generally when you stand your cadence will be much lower than while sitting so that will sway your force development to more fast twitch muscle fibers. That could just be indicative of your muscle fiber breakdown.
I’m sure it’s something that you could slowly change with lots of endurance training to begin to change those fast twitch fibers to more hybrid or slow twitch. But is it something that you think is holding you back or that you would like to change or just that you think is different than most people?
Contador famously was very similar. One sport scientist said if a rider stood up during a ramp test it meant they had less than a minute left but for Contador he could go for another 4 min after standing. Something about his physiology just worked better that way.