...or 100%. But yeah, the MC comes in this way. You have a current most probable value for the position and some distribution around it, depending on the precis

...or 100%. But yeah, the MC comes in this way. You have a current most probable value for the position and some distribution around it, depending on the precision of the measurement device etc. That can be a high-dimensional space. You draw some (many) random points from this space and propagate them all deterministically. Taking into account how likely a certain random point was in the first place, you can then estimate the hit probability. MC is numerically approximating an integral. Here it replaces the high-dim integral over the start parameters.