Overview: Going to break this down as the rules are printed. If someone disagrees then please post page or gw rules errata that states otherwise. Posting this seperate because in a previous post I didn't cite or lay everything out as clearly.
Legal Protections: I am not going to post text word-for-word from the 40K rule book. Any of that information can get the GW legal team to have the ISP to delete the thread or even this forum.
Layout and Dissagreement: Going to post the page numbers and a synopsis of what I understand. If anyone reads it differently please pipe up.
Page 3 Measuring Distances: First paragraph.
So with normal space marines, IG, orcs, and other infantry distances are generally measured from the plastic base and not the model glued to it. Note: with ruins and unit coherency on page 82 being a clearly printed exception.
Page 66 Access Points: First paragraph.
The two inch access range is from the physical hatches/doors/ramps. Not other parts of the hull or down near the treads touching the table.
Page 66&67 Emarking and Disembarking: All text to the section about independent characters.
Models have to be within two inches of an acess point when using said rules.
Page 66&67 Emarking and Disembarking: Both Diagrams
The two inches is shown as a horizontal line at the full two inches from the hatches. Vehicle hatches are not touching the table surface nor are the height of the model bases close to the lowest part of the hatch. The vertical difference is not taken into account by their own example.
Summary: In order to determine the two inch zone for embarking and disembarking measure the two inches flat on the table dirrectly where any acess point would in theory touch if not for treads or flight stand elevating the access point off the table.