Bob,
When I am using powerful or pricey chemicals, I almost always try to err on the side of too light. (Especially if I know I will gear up with that chemical again in a few weeks.)
If you miss a few sections with your hand sprayer, then that will be obvious in a few weeks. Come back in with a spot treatment for those areas. You will then have full coverage for the rest of the season, and you will almost certainly have sprayed less total chemical.
