Agreed. However w/o more information it's hard to determine. If you have an insert with fans that force heated air out, I would consider a bit more or provide some sort of deflection from the forced air away from the tank. However if there are windows between your tank and the fireplace, I wouldn't worry too much.
If the fireplace is along an outside wall I wouldn't really worry about it too much either as they don't tend to be very efficent except for the very near proximity.
Also depends on how big a fire you plan to be running in there. Radiant heat can be quite intense from a big fire but usually they are not sustained.
Good luck and further is better if much of the above is unknown.