Paint flow


Young Tutorling
Ok, my first-ever question. I've had a bit of a search around for answers but to no avail.

The set up:
(i can post photos when I get home tonight if people would like)
I calling it a cheap chineese knock off (airbrush) as it was bought off eBay as a gift for me. It's a dual action side feed and I've been using the gravity type attachment.
Trident paints - way over reduced. Like coloured water.
silent air compressor with a small tank operating at about 8 psi. (trying to keep the pressure low to reduce overspray in my rented house)

The problem:
While practicing a few of the control exercises, I noticed 2 things: my paint had a very definate start point; very hard to build up shades.
I'm guessing the shades have something to do with the paint will only go as dark as the pigment dilute will allow.
as for the former, having a paint start point sounds right but mine ( as it seems to me) my be a little too much of a from nothing to far-out-where-did-that-come-from type thing. Ok, I do have a limited ammount of control over it but I was more wondering over reducing the paint might contribute. Or if the low air pressure could make it worse as well. I've tried playing with the air pressure a bit and didn't knotice a great ammount of change and tried to thicken my paint but was caught with a blockage and cleaned up for the night.

Any observations or comments to help guide me to my problem or probing insights would be wonderful.