Usually when we see then at the bottom (the most common location as Jim has pointed out) it is either to replace an already standing frame post bottom where the it has been comprised in some fashion or it is planned from the beginning with a stone scarfed plinth as illustrated in the link I shared.

I think, in Brent case, the goal is not having to mill or handle a really large long post. This may not be perhaps such a challenge for some, while for others, both wight/size and transport/cost logistics are inhibitive. In this case, after considering also Tim's insight and from past experience, I would centralize the splice and probably make in a meter or perhaps longer, it must be reinforce with adhesive there by rendering the timber virtually whole and solid once again. I would most likely incorporate the through tenon of the "anchor beam to also lock and tighten the scarf. In that scenario, I believe we get the best of all worlds. Two shorter almost equal sized timbers, and good location that works in concert with the other timber joinery. It may perhaps even become somewhat invisible if cut using a version of the recommend kai-no-kuchitsugi (clam shaped splice.)

That, at least, would be my solution if I had to split the timber into smaller size for any reason. I have had this discussion with Ben years ago at Fire Tower PE and noted several more "approved" forms as just described while studying the Asian original forms. I do agree with Jim, that checking in with a PE is advisable if uncertain of ones skill sets in such advanced joinery placement, or at minimum discuss all pro/con with client as it affects cost.

Regards,

j