That first rank of troopers is dead.
With the reach offered by their lances, only half the lancers need be
engaged. The other half (every second, after the first two or so)
remain unengaged.
The troopers _must_ win initiative the second round, or the lancers will
all ride off, and repeat their horrendous charge at their leisure. So
let's say the troopers win, and rush to engage. They can still only
engage half the lancers, if the lancers have been clever. The rest of
the lancers can wheel and charge again.