Hi
There was quite interesting discussion about scarf joints position recently and I suggest you to read it first. Everyone was giving his 2 cents but the conclusion was not clear at all. Some vote for scarf over post, other like it over brace. I'd say it is more like historical versus engineering perspective controversy.
So, your question was about scarf bending strength and you probably wonder why I talk about location?
From the engineering point of view,
scarf should be located as close to place with zero bending moment as possible. In other words it means
scarf has no bending strength. Well, there certainly is some capacity in bending which can be calculated. However, it is not considered either a
"good" nor
"safe practice" to do so.
Unless you orient your scarf vertically indeed. It is probably not the preferred "old fashion way" and also involves bolts & nuts & washers (& shear rings) rather than wooden pegs.As for the placement I suggest to run structural analysis first and than decide where you need to locate your scarf. Because you may not necessary need negative moment over post and thus you may use direct structural support provided by post and have braces handle only lateral loads as they are supposed to.
Very few people actually house braces so the only structural member in play is one peg each side (hypothetically tenon to mortise edge after peg cracks and some imaginary friction between brace and beam/post). Not much, it is barely enough for bracing and takes just one crack to ruin it all. If you are still tempting to place your scarf joint over brace, let me suggest housing the brace on both sides.
Hope this helps
Michal
TFDesign