The website for that case indicates that there are four possible fan locations. Two are the front panel, and used for EITHER a pair of intake fans if you are using a heatsink style CPU cooler, OR a radiator if you have an AIO system. You have an AIO system. Then there is ONE location at upper REAR for an exhaust fan, and a fourth location at TOP near the rear for another exhaust fan. It does NOT show any location in the top near the FRONT, so I'm not sure I understand our query.
MAYBE you mean to say that the one already installed is the upper REAR, and you are asking about that fourth spot in the TOP panel of the case. The manual for the case suggests in its diagrams that, for your situation, you do NOT install that second fan in the top panel near the rear. However, that is an option. Doing that may increase overall air flow potential slightly. However, it also will likely create a negative pressure situation. That is, the air flow capacity of the two exhaust fans near the rear will exceed the capacity of the two front fans on the radiator, because the rad itself impedes air flow in by a small amount. That means that the net air pressure inside your case will be less than outside, so at any leakage points air will flow INTO the case and may carry dust inside. There are ways to reduce this pressure imbalance. If you want details, post back here. OR, you may not think that is an item to worry about, so you could just ignore it.