Excluding the atmosphere, delta vee is exhaust velocity times the logarithm of the mass ratio. The mass of a pressure vessel is proportional to its volume. So i

Excluding the atmosphere, delta vee is exhaust velocity times the logarithm of the mass ratio. The mass of a pressure vessel is proportional to its volume. So if you double the propellant, also tank volume doubles and also tank mass doubles. No clear scale related terms there. Gravity also is not affected by scale, gravity losses are strictly related to mass. But air resistance is different. It is a surface effect and thus related to scale. It's roughly proportional to the frontal area of the rocket. Hence, if you grow a rocket and keep its shape intact, the air resistance grows only as square, but the other factors like mass grow as cube. So bigger rockets have a smaller proportion of their delta vee spent on air resistance losses. That's also why sounding rockets are so skinny. Air resistance dominates there. (They are also accelerating faster since they are rail launched and don't have active gimbal guidance, which makes it even worse) You can think of a medium sized orbital rocket, and then if you shrink it, the only way to keep its payload to total mass rate the same is to keep the air resistance losses same related to the total mass - ie keep its original length and only shrink it sideways.