Why Pixel Depth Offset always push into the scene?

Hi, we I do hair rendering I used a multi-pass method (see…3c9d2490b1.pdf) that render a hair 2 times, first masked then alpha blended. Since I hope Early Z enabled in my second alpha blended pass, I disabled PDO in second pass and changed PDO in first Pass to “pull out” pixels instead of push into, because other wise almost every pixel will pass EarlyZ and drawn - whish is not effective. However there is a comment said “// Can only push into the scene for conservative depth writes”. I know in some scenarios Pre-Z or Earl-Z may discard some pixels, but I think it’s ok for mine. Is there other problems for doing that or other solutions? Thanks.