The pathway shown is just one from an infinite number of possibilities. It is unique because it is the only path which leads to eternal life, but to the people on it at each stage it appears to be only one of a range of alternatives.
There is a serious problem in trying to show some of the alternatives on a sort of map: you either show a route to Jesus from the alternative branches, or you don't. If you do, you imply that "all roads lead to God," and if you don't, you imply that a person who has taken a wrong turning has to go back to the junction they missed before they can progress along the right road.
Sometimes there is a sense in which a person has to turn away from an earlier decision in order to keep travelling towards God, but this happens far less often than we think it should. You and I would probably have tried very hard to convince Saul that throwing Christians into prison was a bad idea. Fortunately, God knows better, and generally moves people on from where they are, not back.
Another thing which should be clear by now is that the scale is not prescriptive. It does not tell you what to do or say. Every person is an individual, and the whole point of the scale is to help you be sensitive to where that person is and how to communicate with them.
The Modified Engel Scale is offered to assist evangelism: not as a tool but as training. We are called as Christians to be 'co-workers' with God, and this requires of us both obedience and understanding. Use of the scale assists our understanding of what God is doing and what He wants us to do.
Possibly the most important thing to remember is that the scale is not intended for presentation to your prospective convert! There are at least two good reasons for this.
Firstly, people do not like being labelled. They do not like to feel they are being categorised. The purpose of the scale is to help you treat them as individuals, and not just lump them together with all the 'unsaved' - and they will not appreciate your explanation that you are putting them into this box because it is much more helpful than the box you would have used before!
And secondly, if your contact is not completely put off by the concept of the scale, you will probably end up discussing the scale, justifying it, suggesting alternatives, comparing the strengths and weaknesses of the different options, and so on. Anything, in fact, except presenting Jesus. We are not called to explain the scale, we are called to present Jesus to them.
We are called to present Jesus. Could this whole discussion be one big distraction from that simple object? Clearly, I do not think so. To present Jesus to someone, the pair of you have to speak the same language. You may be intending to present Jesus, but if you speak a different language your words are meaningless. You can explain the gospel to someone at level -12, but unless God steps in and does another 'Road to Damascus' job, your words will be wasted: they are not in a position to understand what you mean. You need to pray and try to communicate the presence of God as a reality in your life - to communicate that He is not just a figment of your imagination or an externalisation of your subconscious desires.
We are called to present Jesus. We are not called to criticise, attack or demolish the alternatives to Jesus. Evangelism is inherently constructive, not destructive. We are not called to convince people that Islam or Buddhism or Communism or Materialism is evil, wrong or inadequate: we are called to offer them Jesus. Once they see Him, they can make up their own minds.
There is a little truth, a little light in almost every religion and ideology that people cling to. Don't attack the candle, just let in the daylight. No-one relies on the light from a candle when standing in the sunshine, but until people see the true light they would be foolish to give up their candle.