I'm not a cav myself, but when I saw public polearms statistic, it was clear that 95% of lancers prefer Heavy lance.
I think that such advantage is not healthy enough.
My suggestion - every shorter than «heavy lance» lance must receive some bonus to «lancer arc». Not big, but something to encourage people to diversity.
Example:
If heavy lance have 30 degree effective arc>
Then Lance must have 33,
Light Lance - 36,
Doublesided lance - 39
Discuss?