I top fill mine . But make sure you cover the air holes . Then make sure the top cap is threaded a little then turn it over and continue closing it . I will leak a little just keep hitting it until the vacuum seal is good.
I'll just add that if you're gonna do it this way, after you get some threads started (and you make sure the top of the chimney is at least touching that top o-ring), plug all 3 holes with one hand (the two intakes and drip tip) and flip it over, use your other hand to remove the fill screw before screwing the cap onto the tank. This allows the tank to vent air out through the fill hole instead of trying to force juice into the wicking channels into the chimney. All that pressure has to go somewhere. If you don't do this, you'll lose about a ml or more through the chimney. Top filling is quick but dirty. You'll lose some into the chimney every time no matter what your technique. Been there done that. My juice costs too much to waste, so I'll use the fill port, hold the tank at an angle and tap the air bubbles out... it's painstaking but I lose no juice. Takes 5 minutes to fill it to full capacity (4 or 5 ml). I look at it this way. At least I'm not carrying around a bottle/dripper all day. To me that's ludicrous.
The problem with the V4 is that the outer diameter of the chimney isn't much smaller than the inner diameter of the tank, so liquid has a tough time settling to the bottom while it's upside down and you're trying to fill it and get the air bubbles out. It's worse if your juice is mostly VG, like the majority of premium juices are. Most of the time I use my Orchid V2, which doesn't have this problem at all because of the bigger tube. Liquid settles to the bottom instantly.
