Good questions. POH says 25 degrees for short fields. But to your point, that feels "risky" in the event of an engine failure upon takeoff. 10 feels like a better compromise, but I can't say I've tried it. My guess is 10 degrees doesn't do very much with our type of flaps. Flip side, if you lost an engine it may not "hurt" as much.
Someone else who has operated a Seneca from short strips please chime in.
