关于-ing分词分句与限定从属分句的转换关系

（章振邦新编高级英语语法543页。）

Since being in the army, he has been in much better health.

=Since he was

=Since he has been

请教老师，以上果真是相同的意思吗？

我在薄冰英语惯用法词典945页看到：

since he was in the army = 他不在部队里。

since he has been in the army = 他现在还在部队里。

since being in the army = 他在不在部队里都有可能，并且此时since是介词，后接V-ing , 这种形式since v-ing 罕见。

如此看来，章振邦的说法和薄冰的说法似乎矛盾不同？

请教专家老师分析，非常感谢！