The mast setup/headstay tension is going to be a combination of your backstay tension and the checkstay tension. Also your checkstays may be multi-part (two or more connections to the mast combined to a single purchase on deck) If so each section will be adjustable separately. You can use this to fine tune where the mast bend takes place.
The harder the checkstay is on, the less mast bend you'll get, and the more tension will be transferred to the headstay. But BE CAREFUL - it's possible to put a reverse bend into the mast with the checkstays if someone gets carried away. This makes your main look like SH**.
So experiment with various settings, and mark them somehow for future reference.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)