Found it, page 12 and page 158 covers models and bases stating that if they are hit partially or fully are counted as hit for template and large blasts. But to target the model the range to the base must be met and the blast marker hole must cover the base.
It appears though that template weapons don't need to hit a base for the target also, they hit any part of a model as per the rules on page 12 and page 173. They just check range to the model and base.
Page 12 seems to clarify the issue for me most and it's at the beginning of the book! The most neglected part of the rule book
The book constantly references back and forth between models and bases stating to measure from base at all times on page 10 for models and units. Then states unit coherency is measured from the model and so is firing but when an enemy targets you they need to hit the model. It's not clear on how to measure distance. It's confusing because our jet bikes come on tiny bases that don't match the model like space marine bikes do. Anyone have a clearer explanation for this? Thanks