I guess I am wondering why the SWR change?
A textbook loop is a balanced antenna relative to ground... All portions of the wire are as above ground as all other portions. Coax is an unbalanced feedline as one side of the circuit is grounded.
If you have a perfect loop fed through a perfect Balun presenting a non-reactive load to the tuner the length of the coax shouldn't make too much of a difference. But we'll never know for sure because you don't have a perfect loop. That does not present 50 Ohms resistive to the coax. Which means the feedline is operating with an SWR that could make it go gnarly at some frequencies (that's a technical term). Further, in another thread you mentioned operating on 40, 20 and 15 Meters. Which means if the loop was near-perfect on one of those bands the odds are it would be imperfect on the other two. With a capital 'IM'.
When you use a tuner the only part of the antenna system that's 'matched' is the coax between the tuner and radio. The coax between the antenna and tuner comprise what's often referred to as a conjugate match and the coax is as much a part of the antenna system as the loop itself.
So, yeah, if you changed the size of the loop you'd expect a change in the tuning. Same deal if the coax length changes...