Post-Relationships

Ok. I've just read through howto:post_relationships and I'm wondering if these are hard rules there or if they should always apply.
Case in point are doujin_covers and images showing the same motif, but without the text and that are smaller.
Like post #2575094 and its parent version.
@Mikaeri post is much smaller (i.e. has less resolution) but it has no text.
My post is bigger but it has the text.
So my question is: Shouldn't it be this way around if there is a cover page and the same image without the text that the version without the text (i.e. no watermarks) is becoming the parent version?

I usually parent the cover with text if it's a larger resolution, since resolution > watermark as follows.

Definitely broken this rule a few times before though, but only because it's rather difficult sometimes to tell which ones should belong.

The question is if this specific rule shouldn't be changed for doujin covers since the text is often times really obstructing :3.

For myself, it really all depends...

It's usually a subjective judgement call based on multiple factors, such as size, cleanness, text, watermarks, etc.

As for your specific question regarding text, it should factor into the decision but not necessarily be the deciding factor.

Examples where I'd choose the text version over the text free version...

1. Much larger version
Text-free: 640 x 480
With text: 1280 x 960

2. Cleaner version
Text-free: Scan with lots of artifacts (JPG)
With text: Digital copy (PNG)

However, all things being equal otherwise, I'd choose the text-free version over the with text version.