BYB, as I remember it, (because I don't have the Jepps to hand or come to think of it, the AIP) the SHJ and DUB CTZ's are surface to 1500' on top of which the Dubai CTA begins. Therefore I would suggest that at 1500' for crossing SHJ centreline / extended centreline, you should be with SHJ tower any higher then you would be with Dubai Radar and of course SHJ doesn't know you are up there.
Regarding the above, I suggest you ask one of the instructors at EFS for a copy of the plan view of DUB and SHJ CTZ from the AIP.
Cheers,
F-S