Hi

SWIMS first try with 150g powdered mimosa resulted in 0.5 g crystals (a bit yellow). The main reason for the lousy yield was that SWIM didn't wait long enough and tried to speed up evaporation a bit to much

Now SWIM is doing a second round with approximately 700 g powdered mimosa, following Normans tek but with only 5 L waters instead of the 11L that is proposed.

Will the reduced amount of water result in a lower yield? The reason is that SWIM didn´t have enought lye home so he calculated how much water could be used to get a PH of 14 (using http://www.sensorex.com/support/more/ph_calculator).

I don't know the answer to your question but you can still go buy NaOH and add it (with water) afterwards.

The amount of lye called for in that tek takes your water WAY past pH 14. The pH isn't the point, that much lye is needed to break down the plant material. If you want to use less lye, do an A/B.
The amount of water called for is to keep the solution free flowing enough that the NP can separate. Sometimes 1 1/2 to 2 times that quantity of water is required. I don't know what will happen with your particular extraction, but don't add the NP if the solution looks thick.
Both of these issues specifically regarding this tek have been discussed at length on this forum.
I would highly recommend that you do some more reading before trying to extract a large quantity of bark.