Representation of W Frisian <tsj>

Do you have any views on what the phonemic representation of West Frisian <tsj> should be? West Frisian phonology doesn't include it but would suggest /tɕ/ (as <t> + <sj>) whereas the WFT and a few papers I ran across on Google use /tsj/.

So far I've just used /tsj/. [tɕ] is not a phoneme for the same reason as its Dutch equivalent: the change from /t(s)j/ to [tɕ] is automatic and happens not only across morpheme boundaries, but across word boundaries.