Hello,
I think the algorithm description is pretty clear:
Flood ping. Outputs packets as fast as they come back or one
hundred times per second, whichever is more.
So on fast links , you can see >100 pps, the smaller the ping size, the greater is the achieved rate.
On slower links, it is dropping back to 100pps, and once 100pps is met, it stays there.
Also, there is low-prio traffic throttling on RE-PFE link, and pings are assigned to Q0/best-effort on that link in PFE->RE direction.
So if there is other control traffic going across RE-PFE link, the pings may slow down even more.
This may explain Your observations.
HTH
Regards
Alex