usually most dirt is sat on the surface of the fabric so just rinsing the top will leave it clean without having to penetrate all the way through the fabric.
the solution need to remain in contact with the dirt until it dissolves and emulsifies it leaving it in a liquid state able to be vacuumed off the fabric, the prespray will do most off this work, but not all of if ( otherwise a cloth would be able to remove the dirt without any rinse)
your tool is'nt allowing the solution to sit on the fabric long enough for for this too take place, without holding it in the same position for a length of time which will cause you to empty your tank very quick
internal jets are not that good, when used with low pressure portables the solution does'nt have the power to fight the vacuum.