Filling 80W90 lube (with anti-slip additive) to the bottom of the side hole is the way ZF says to do in all their manuals. I find that system to be sloppy with a flexible funnel, which is why I rigged up my adaption of the elbow/dipstick. As I mentioned, a few oz more or less is just fine. You'll get that much variance with chassis stance from excruciatingly-level.. Don't worry about it.
The lube is so thick at room temp, you'll get some drainage every time you pull the plug. And way-too-much is self-regulating thru the top vent hose. But it would take a massive mis-measurement to overflow out the top, even when hot & expanded!