I feel the devs may want the Chinese handmortar similar to culverin so added 6x damage multiplier against Siege Units.But I think this will make it too strong.For example,now they are very effective against Steppe rider and Oprichnik,etc.And to the Monitor,it can cause over 400 damage by one shot.That is unacceptable.
My idea is:
1.Add the 4x damage bonus to multiplier against buildings.
or
2.Add their speed to 3.3
or
3.Add 50% basic damage.
Or both 1 and 2.Or both 2 and 3.