Thanks for the free lessons everybody.
Sinew is pretty forgiving so it doesn't matter too much how you apply it in a small area. Large areas require more careful placement.
If you are using good quality hide glue, the thickness won't matter and there's not much danger of cracking later. I've seen cracks develop, however, in really thick sinew while drying. Wrapping the sinew with an ace bandage while it's drying will solve this problem.
If I do get a crack, should I ignore it, or fill it later, or sooner?
There isnt any reason to build thickness up in one area and not the whole back, no that I can come up with anyway.
PD, I was thinking I could build up allong the sides of the middle row and cause a little less crown on this shagbark sappling that is 60" with a flat belly, and create more working neutral plane. Would having a more flat back be beneficial??
Once again, thanks folks. All of you guys knowledge has been amazing to read through over the last year.