Hi
For sure, there could be a problem with TPXO data particularly if you model is too local and in an area where the TPXO coverage is poor...
Could we have an idea of the outline of the model you run, in both case?
If this is the case, one solution could be to enlarge your model in the persian gulf.
Another option more used in the past, for such local studies when the computation capacities was rather limited.
The method was to build a quite large model with not a too high resolution to have a limited number of node. Run this model first, and extract the boundary condition for the local fine mesh...