I think your problem is your using the wrong machine, try using your 19" machine.
For best results on some really dirty carpets, vacuum, pre treat with punch and if you have a shower feed tank on your rotary use it to apply the DS using a fiber plus pad. If you don't have a bucket heater buy one put it in your tank and let the water heat up while you set up and vacuum do this before you add the DS to the water.
Shower feed the hot DS solution onto the carpet working the machine in a oval patteren the best you can, I like to work my way into a room then use a micro or cotton pad to work my way out, then groom.
I think the results you'll get will make the most picky customer happy.
Also if weight of the machine is a big issue you might consider the BrushEncap machine Rick sells.
For best results on some really dirty carpets, vacuum, pre treat with punch and if you have a shower feed tank on your rotary use it to apply the DS using a fiber plus pad. If you don't have a bucket heater buy one put it in your tank and let the water heat up while you set up and vacuum do this before you add the DS to the water.
Shower feed the hot DS solution onto the carpet working the machine in a oval patteren the best you can, I like to work my way into a room then use a micro or cotton pad to work my way out, then groom.
I think the results you'll get will make the most picky customer happy.
Also if weight of the machine is a big issue you might consider the BrushEncap machine Rick sells.