I been using jectronic valve in non proportional mode for the brakes....the trick is to use it putting a Robart restrictor about 6 to 8 inches before reaching each tire.
This produces a smooth stop effect...

The distance to install the restrictor before the tire is critical. The remaining air line between the restrictor and the tire will work as expantion chamber were the air preasure will build up slowlly until activate the brakes O-Rins. By shortening this line...the preasure will build up faster reduding the smooth effect.

Mi 2 centavos....