What are you using for -Rw/e/s/n and -Idx[/dy]. I see your search radius is 10km but that is a separate parameter. Perfectly possible to ask for a -I30s 30 arc-sec grid and use all data inside a 10 km circle centered on each node. If radius is significantly larger than cell size then it basically does filtering. Remember we search for all data points inside those circles and they do look different than what blockm* modules return on a per rectangular bin basis.
It sounds like you imply you want blockmedian -T0.95. But, would like to know what -R -I you used in case I can hunt down an issue>