Sizing secondary deployment charges

I could use a bit of advice on sizing secondary deployment charges.

Rocket is 6" diameter, dual deploy, three #2-56 shear pins attach the nose
cone, 20 pounds total weight. In ground testing I got a nice clean
ejection
with 1.75g for apogee and 2g for the main (ffffg powder).

I've heard folks say they use 50% additional powder for the secondary
charges, but that sounds excessive. I was thinking more in terms of 10% -
but is that adequate?

Kevin