Well...
...the first boat I had for almost two decades had a bendy rig with the forward lowers removed which was common practice. And, yes, tightening up on the main did, in fact, add some headstay tension. Same with the second one which was a free-standing rig. My current one has aft-raked spreaders and there is some increase in tension when the main is tight, but no where near what the other boats' rigs exhibited. My sail maker advised me that he cut the jibs to allow for some headstay sag that was common on (these) fractionally-rigged boats. I recognize this is is contrary to fractionally-rigged boats with runners or masthead rigs, but I doubt it's otherwise all that uncommon. Rick D.