Jeff, this wouldn't have anything to do with the choke settings. I don't have dtg rip pro, but it's made by the same developers of our rip, so the controls should be similar. In the white creation area, there should be a slider for the sensitivity of white ink. It's probably below the drop down menu for how you want to create your under base (i.e. use transparent background). Slide that all the way down. Even though your on screen preview will look very dark, don't worry about it, the print will come out fine.
If that doesn't work well enough, you can create your under base in Photoshop and import your white layer into the rip. This will give you much better controls. You would need to create the page the way you want it to print and in the correct position, and create the white under base in the same file. Then save the white under base and color layer as two separate files. When you import the color layer, don't move the position on your copy board and then import your white layer by choosing the appropriate selection under the drop down menu in the white generation area of your rip. It's a few more steps, but if lowering the slider doesn't yield the results you want, this option will.
Of course, this is assuming the controls are similar to our rip.