Height Map experiment - answers required!

I am doing some experimenting with Height maps in MDB version 1.8.2

Above are two images using the same parameters, but where I have inverted the map I made. The top image is where most of the map is white (ie not the brush pictures) and the lower one most of the map is black

Brushes from:
Star: [link]
Ruin: [link]
Camels: [link]
Grass: [link]

I can't find any tutorials around height maps and I am wondering what some of the settings do.

What effect do these have in height map settings?
Map channel
OTrap Channel
OTrap offset
OTrap multiplier

Also is there any way of stopping the repeat of the map in an image, as I had to zoom in to this to take out the repeated effect.

Many thanks for any help/comments