I quoted your post because you were responding to ron hudson who was questioning how he could measure the tension on his furlered Forestay. IMO the simple answer is: You can't. Also confirmed here:
How to use 90 & 91 Series Tension Gauges
I don't think the Forestay tension should matter as long as :
You have proper mast rake, correct forestay sag, and don't exceed the maximum tension limit of your backstay. I don't understand what the 1.25 number does for you.
The quote from the gage instruction is "Backstay tension would, of course, have to be adjusted to maintain a straight mast with the desired forestay tension. Since the backstay makes a greater angle to the mast, the backstay tension will be lower than the forestay tension.
NOTE ! ROLLER FURLING CAN ONLY BE SET BY BACK STAY TENSION."
That is what I said, you cannot measure directly forestay tension, but you can calculate it based on the angle of the backstay and forestay, and since you know backstay tension it is a simple calculation to calculate forestay tension. And forestay does matter if you want to keep your stay tensions below say 20% UTS. Because of the 1.25 factor, you will want to keep backstay tension at 16% to have a forestay at 20%. Note this is for my rig, others depending on stay angles may be different. In order to change mast rake, you can change the length of your forestay (and keep tension the same), my rig has an adjustable plate at the bow connection where I can move the connection to vary forestay length.
If you take your back stay to your maximum desired tension, your forestay will exceed that amount by 25% (again, based on my rig dimensions). If you are trying to keep the tensions below a certain value, then it is important to know this value is higher on your forestay and therefore need to reduce backstay tension accordingly.