It's probably consistent with historic English usage, but the two places that still officially use it (þ and ð in Icelandic, ð in IPA (which uses a different character in place of þ) do it like ðat so we might as well learn from ðem! Also, Þ is a capital letter, most English words would use the lower case þ.

But boþ of ðose only matter if you do it for spelling reform reasons, which is not Sxan's stated goal.