We can talk about the elements of rig design if you like. I could do a short primer on how to design a rig. You decide.
You have a round mast. That was common back in the old days and often the spar was a solid, tapered pole. Atkin's designs in the Ideal series are typically rigged like that. But with a box section laminated spruce spar you can have longer fore and aft panels
(sides) of the spar and shorter athwartships panels (front and back) This is what you need because the fore and aft moments greatly exceed the athwartships moments due to the simple fact that you have more shrouds than you have backstays anf forestays. So the fact that you have a round spar means the stick is either way to big for the athwartships min required moments or it's way too small for the fore and aft min required moments. It can't be ideal for both. Based on what you tell me about your mast bend situation I would deduce that the forea and aft moms are a bit on the anemic side on your mast.
For the record:
I think the stay that goes to the masthead is the "headstay" it goes to the head of the mast.
I think the inner for and aft stay is called the "forestay" because it's forward of the mast.
You may think different and you might be right but it would simplify things and help communication if we could agree on some terminology.
I have seen three applications for running backs  boats with booms to long to allow a fixed backstay  to tweak mast bend/sail shape and  to counter the effect of a forestay in heavy weather "pumping".
Rigging consists of headstay, forestay, lowers (1' forward of mast), intermediates (3' aft of mast terminating at forestay), running backs (terminating 2' above forestay) and cap shrouds, backstay. If you draw the connection points around the edge of the boat from above it appears all rigging is pretty evenly distributed.
I was using the term William Atkin used in a description of this boat topmast stay (which if this were not a knock about would have started at the masthead and terminated at the end of the bowsprit) and the head stay which starts at the stemhead and goes terminates 2/3 the way up the mast.
Mast construction was three layers of wood laid on top of each other, glued and shaped,the mast bend is from a bend built into the mast in manufacture...the flex is something different, and to accomplish that it is a combination of the overall tuning, lowers pull forward while intermediates pull back (put it where I want it and leave it), runners were not intended to tweek mast bend/sail shape, rather to give a better angle of pull than a backstay in a boat that had a boom too long to accommodate a backstay anyway.
Mast measures 6" diameter at the deck, the most significant taper is in the top few feet of the mast...The builder did not have a need to whittle off a few ounces of wood for racing, his intended use as was that of all future owners was ocean cruising. Alot of the aspects of the boat are over built, I would think laminated Sitka Spruce (probably using Resourcenol), being stronger than a solid spar would be one of those.