The value given in Vizzy by Performance -> Max Engine Thrust is subtly wrong. It doesn't take into account the Max Engine Throttle setting accessible in-flight by the part inspector. That is, it gives the correct value when the default max throttle is at 100%, but doesn't scale it up or down when the max throttle is changed.
Oh boy the devs are gonna not like you, boy! But your right, I think even an apoapsis circularization burn delay would have a similar effect on the Δv tho much smaller variable than lower in the gravity well with all that friction too