That is plenty full. You should only notice that the tank doesn't feed the carto as well when it's almost empty.
Are you using the pre-punched carto that came with the tank? Bc if so, that could be part of the problem. The eGo is only 3.3-3.4V and dual coils really arnt that great at lower voltages. I use a smoktech 3.5ml tank too and while the dual coils are alittle better on a 3.7V PV, their still nothing special. I took the DC that came with the tank out and didnt even use it. I use the 1.7ohm Ressurector cartos in the tank which are single coil and they work a lot better. You can punch your own or CCV sells pre-punched Ressurectors for the Smoktech tanks, and they even have the metal base on them like the carto that comes with the tank so the tank can't slide down. I would try them bc I think you'll like them a lot better.
Popping and crackleing Doesn't necessarily mean the carto isn't wicking well, and normally popping and crackleing is a good thing bc that means the atty is wet. All new cartos pop and crackle, but it will tone down once you break it in.
The hole in the pre-punched cartos is small, so some juices wont wick as well. 65/35 isn't too thick and it should wick, but the tanks def not going to feed the juice as fast as if you were using a juice that was like 80/20. I have 2 3.5ml tank and I use a juice that is 80/20 in one tank and it works great. The pre-punched Ressurectors have the same size hole and the tank feeds the 80/20 juice to the carto very well, sometimes even almost alittle too well. My other tank is filled with Bobas Bounty and the small hole in the pre-punched Cartos I doubt would even let the tank feed the carto at all bc Bobas is 100%VG and very thick.
For a juice that is thick, I punch the hole a lot bigger so it feeds into the carto much better. The juices I vape are normally 30% VG or less but I do really like Bobas, even though it is 100%VG and thick. To make it work well in a tank, using a finishing nail and a hammer I make the small prepunched hole much bigger, and actually punch a second hole on the opposite side as well that is the same size so then the thick juice feeds to the carto much better, and the 2 holes allows the tank to keep up so the carto doesn't get dry. So if you feel the juice isn't being fed fast enough, you might need to make the hole a tiny bit bigger so it feeds quicker. 65/35 isn't that thick though so the hole wouldn't need to be much bigger and it def doesn't need 2 holes. Be careful bc if you make the hole too big, it will just flood the carto. Scottinbocas advice is spot on and you should try that before you try to make the hole bigger. Without pushing the button, take a few short fairly hard pulls on the carto. Doing that will feed juice to the carto. I always periodically do that with both my tanks to ensure the carto stays wet. Look for tiny air bubbles to come out of the hole bc that means juice is being fed to the carto. If you don't get any bubbles, then it could mean that the hole is too small for the juice that your using
