I think your time values may be off by one zero. 800 is going to be 800ms, not 8 seconds. Try 8000, 16000, 24000, etc., rather than 800, 1600, 2400.
<.. a few moments later..>
I just checked my inbox and saw that you actually wanted the probes that close together! No, it won’t let you do that because then you end up with probe response confusion--i.e., you don’t know which probe an rt is associated with. I think there is a minimum amount of time that can pass after a probe occurs at which point it will be considered a missing response.