be careful there: Croatian mainland is a mix that include area as far as Zagorje (north from Zagreb), Osijek (east Slavonia close to border with Serbia), and Dubrovnik (very far south close to Montenegro)
J2 did spread along sea coasts mostly... my guess that in area of Liburnia it is around 11% as Island of Krk is close to mainland area of Liburnia...
Brac, Hvar and Korcula are on the map of Liburia south most islands, very far from Liburnia mainland.... I do not think they can be used to extrapolate values for whole Liburnia because those 3 islands are quite separated from the rest of Liburnia and for instance has I2a2 around 55% while island of Krk on north of Liburnia has 9.5% I2a2
besides, area that looks as a hole is exactly the settlement of Croats according to
http://www.euratlas.net/history/euro...tity_1523.html
which further complicates interpretation of the supposed hole in J2 spread...
I have even heard discussion that J2 might have been main marker of Liburnians before Croats settled the area
also if you look at variance for J2, it is pretty high along sea coast in area of Liburnia