主句与从句的相对位置不同会影响是否用逗号吗

关于你的问题，基本原则是：如果主句在状语从句之前，通常不用逗号；如果主句在状语从句之后，通常要用逗号。

但这并不是绝对的，实际语言是丰富多彩的，例外的情况也有很多，你举的例子来自新概念，下面我给你举几个词典的例句：

1. 状语从句在主句之前没用逗号的句子：

(1) When I turned round he was pointing a dirty great gun at me. 我转过身来，他以一支老大的枪对准我。（牛津）

(2) When he spoke I was expected to reciprocate with some remark of my own. 他在说话时，我也应该说点什么作为回应。（朗文）

2. 状语从句在主句之后却用了逗号的句子：

(1) She made herself get better by sheer willpower, when everyone else had given up hope.  当所有人都已经不抱希望时，她仅凭毅力恢复了健康。（朗文）

(2) She thanked her lucky stars that she had taken out insurance, when she was in an accident on holiday. 当她渡假出意外时，她庆幸自己办了保险。（剑桥）

(3) Newton reasoned (that) there must be a force such as gravity, when an apple fell on his head. 当苹果落在牛顿的头上时，他推断出这一定是由于某种力的缘故，譬如重力。（剑桥）