After exposure, the stencil will still absorb water and swell up. When it is swollen with water, it is very vulnerable to damage such as scrubbing.
ZBF Screen Making Manual
ZBF Screen Making Manual
If you have to wash out your stencil outside, do everything you can to protect your precious stencil from UV energy that can flash the surface and make washout more difficult once you have taken off the positive.
You are not going to find any difference between capillary film and direct emulsion, but you will have a difference between the sensitivity of individual stencils.
A very fast emulsion like Ulano QTX will be more sensitive than a slower emulsion like QX-1.
Make a test. Block off an area of unused stencil with something that will block all exposure like a shirt cardboard or Rubylith. Take a scrap positive and tape it to the unexposed area AFTER you have exposed the stencil with your actual job positive. Pull it off as you start to spray with water and you will see if any exposure is taking place as you move the screen to your washout area.

Nassau December 2002 - sink not installed yet

Look, using a street light as a back light!