patty,
1ppm is no problem to soak in, the plan for dichlor dosing is to get down to near zero when you want to soak.
You don't want to leave your free chlorine level at zero for very long. But as long as you are controlling it you get it down near zero when you soak and immediately after soaking you add dichlor to kill anything you may have introduced into the water.
I wouldn't think it's at all unusual for a tablespoon of dichlor to raise your FC to 5-10ppm if your tub was already really clean, nothing in the tub to burn up the FC. Although 5ppm isn't really that high, not sure which end of the 5-10ppm scale you were really at. Some folks consider 5ppm as the minimum you should get the tub to after soaking (especially if you don't have some secondary sanitizer like ozone or N2 in use). If you have a secondary sanitizer than 3ppm may be fine.
Every tub is different though. Depends on size, usage and how much yucky stuff is introduced into your tub. It may take a while for you to figure out your tub's chlorine demand, if it's really clean (what you want) then just a small amount of dichlor can bump up your FC pretty easily.
Steve