This is probably one of the most contentious of the CE events, apart from deciding on the effects of a 'weather event' CE. NEC4 does not alter the wording under either clause 60.1 (12), 60.2 and 60.3, so the tests remain the same as NEC3.
Firstly, 'physical conditions' is not defined, as you have said, and is often associated with ground conditions, which is not surprising considering the ICE origins of clause 60.1 (12). It must be within the Site (above or below ground) and be 'encountered', implying a direct encounter, such as the discovery of the utility in your case.
The clause operates on the assumption of an 'experienced contractor' at the Contract Date, applying a test of 'small chance of occurring', factoring in 'reasonableness'. So you assume the position of an 'experienced contractor' and consider what is likely to occur, based on your experience of undertaking similar works in similar conditions. You then decide how likely the 'physical condition' is to occur and then make an appropriate allowance accordingly. The CE assessment is based on the difference between 'actual' and 'ought to'.
Any information regarding sub-surface conditions should have been included in the Site Information (SI), not the Works Information (WI). As the PM does not have authority to instruct a 'change' to the SI then the matter would be a 'physical condition' CE. Having said that, I have worked on projects where the information is in the WI, and also where it is included in both (how do you resolve that one) !!
As much as the applicable clauses apply 'objective tests' there are still elements of subjectivity which lead to a difference of opinion. As a Contractor you can help yourself by documenting included allowances (or why an allowance wasn't made) , which comply with the 'at the Contract Date' test and also provide a basis for constructive dialogue.
As to the question of how far the utility is assumed to be from the line on the drawing, clause 60.3 is a 'warranty' from the Employer as to accuracy. If this doesn't apply then the tests above will come into play.