its for ether... most binders have adjustable heel cups though.
I think something else is up 155 eve has a 25.1 waist and a 7.0 side cut, the SL has the same waist, and tip/tail width and a wider 7.5m side cut (minor but would increase over hang) . How are you fine on one and wack on the other??
are you using the same boot, binding, and stance and angles?