N.B. The email exchange below may have been edited, e.g. to remove content not essential to the main point(s) or to standardize English spelling/grammar.
...in terms of the geographical area Macedonia, Samuil's Kingdom does not overlap entirely with the geographical region Macedonia. Yes, it's got a part of it included in his Empire (the other bit is in Byzantium), but Samuil's state is by no means "Macedonian" in any way -- geographical nor political... I'll send you a map so that it can be seen [more easily].
Encyclopedia Britannica says, of Samuel, "Ruling originally in Macedonia, he then conquered independent Serbia and further extended his power into northern Bulgaria, Albania, and northern Greece" (1980, VIII, p. 837). Stated bluntly, Samuel extended his rule from Macedonia to include the Bulgarian empire. Your map, which appears to come from the Wikipedia article about Samuel, shows the Bulgarian empire -- but not at its maximum extent, which according to that very same Wikipedia article included "most of the Balkans (with the notable exception of Thrace) as far as southern Greece" -- loosely, from the middle Danube to the Peloponnesus, hence everything that could then or now be called Macedonia.
Horace Lunt's reference to "the Macedonian king Samuil" is consistent with the EB account, and it was not very long after Samuel's large territorial expansion that he was officially crowned Tsar of Bulgaria -- hence our original choice of the title "Tsar of Macedonia," which is also consistent with at least one thread of history by which Samuel was of Macedonian descent. Even Wikipedia [as of today] admits that Samuel "is regarded as a heroic ruler in Bulgaria and the Republic of Macedonia."
However, to forestall this and at least some future objections, I have changed our Old Church Slavonic Online introduction to read as follows: "...erected in 993 by Samuel -- of Armenian ancestry according to one primary source -- who later became Tsar..."
P.S. (Oct. 15, 2010) See also our Blog response to issues re: Samuel's culture/ethnicity.