I experimented with it and got similar results - I don't know why I was slaving away so hard over inferior builds...
Its crazy how hard a couple of reaper instances can go.
Pro tip: if you don't care about any particular unit (that has nimble), chuck it into the reaper grinder - it still gives the stats on the first instance, while giving two procks of the ability (if there was a chance to attack twice). If not, you still get the stats and can keep the other potentially stacked unit (nimble blocks the 999 damage).
Beware!
I didn't know reaper was one of the traits that could randomly be gained on level up, costing me a unit with over 100 att and 35 hp (earlier this run).