Indirect films are processed off the mesh, so they require a balance of hard and soft so they will adhere to the mesh after development. Too much exposure and they will harden, but not stick. Not enough and the will dissolve and rinse down the drain. Each step on a Stouffer 21 Step scale will be a different color. Aim for a 'surviving' Step 6. No 7 step, and darker steps as the guide number decrease.

Underexposed: Look for a lighter color. Stencil will be thin (and look thin) resulting in poor press endurance. Underexposing for resolution sacrifices durability. 

Overexposed: Stencil will be thick (and look thick) resulting in poor adhesion due to over hardening.