When JTAC says they are "heading east", that means they are heading to the east from their present position. The tanks could be to your north, south, east, west, or wherever, so this information is useless unless you already know where the tanks are in general. JTAC doesn't really know where you are exactly, so they wouldn't be able to tell you where your target is in relation to your present position. This is why they give you a 9-line - so you know where the target is and how to safely approach/engage it.