I was doing some research, and noticed a bug in visualizing area of monsters with local spawn. I suppose RMS parses (e/r)athena format of permanent monster spawns. For instance, this defines permanent monster spawn for 7x Sandman, with 60s respawn timer in area 130,225 +- 46,59:
ve_fild05,130,225,46,59 monster Sandman 1165,7,60000,0,0
RMS visualizing mechanism supposes, it's a rectangle, with center in 130,225, width 46 and height 59, thus rendering a rectangle (130-46/2, 225-59/2) - (130+46/2, 225+59/2). However, the second pair of coordinates does not define width and height, but rather span of that rectangle, so it should render (130-46, 225-59) - (130+46, 225+59).
One can probably find proof in (e/r)athena source code, I claim that from my personal experience (e.g. Kasa in thor_v01 in upper right corner are shown 99% in the wall by RMS).