Axl Kowalskii,
I don't mean to offend, but are you a type qualified and line released pilot? If not - that's fine and it's great you are seeking further understanding about performance and interpreting the RTOW charts.
If however you are a line released pilot.. then it is rather worrying as pilots in your airline either are unclear about the SOP or worse your airline has the SOP's exactly as you describe and are not meeting the minimum performance requirements on some takeoffs - thus invalidating any obstacle clearance and RTOW calculations.