There are no HDB blocks between T3 and SICC. The HDB blocks are on the Sin Ming side, so only the south-facing units will have to clear that. The HDB blocks are eleven storeys, but T3 is on slightly elevated ground, so I presume those on eleven and above will be able to see beyond the HDB blocks. As for the north-facing units, you will need to be above seven to be able to see past the trees and low-rise private estate; not sure how high one must be to see the reservoir on the other hand. Also, the north-facing units need to account for Thomson View. From my survey of the plot, Thomson View lies to the left of the plot (when facing the main road), so only those units which face slightly to the right will have an unblocked view of SICC.