Don't forget the reason for deploying flaps when landing is...
1. To reduce the stalling speed, so that aircraft can be flown slower.
2. Move the stalling area of the wing to the root section. The wing-tip will be at a reduced AoA, so that it is not likely to tip stall and cause a spin. The wing-tip will therefore create less vortex.
The question says each aircraft is flying slowly, but maybe the first one will be flying slower that the clean aircraft.