I'm a mechanical engineer and I work sometimes in a very busy machine shop. I think you're over-thinking this ramp operation. Ramp entries are great, but the first consideration is what ramp angle can your cutter handle. This is specified by the cutter manufacturer, and you respect it or you damage your cutter.
So, from this standpoint, by trying to compute this angle in software based on the requested Z level plunge depth, you take away all the certainty required by the machinist to respect the tool capabilities and specs, and you force him/her to pull out a calculator to make sure your software isn't going to ruin the cutting tool.
Thanks for your insightful comment. I agree that the specified ramp angle should be respected at all times.
The angle is not calculated by default, but given as a parameter. The issue is about what to do when the given cutting path is too short to to reach the desired Z with the given angle. My initial quick solution was to tighten the angle, which is, like you said, a wrong one in many cases. The better solution should be to go back and forth until the Z is reached and I already implemented that to my "method 1" and will try to implement it to the others as well.
The discussion about effective material removal and adaptive clearing etc. is a big topic and deserves its own thread and guys with big brains.