ALL warmoth necks have a fender heel, they have several nut widths whack are available with your choice of back contour, back contour has nothing to do with the width of the fret board so the fact you asked in reference to that may have thrown some people off.
if you get a stock fender nut width then it must have the same with at the 12th fret as a fender, 1-5/8" for vintage, 1-11/16" for USA and other models can be either/or.
the neck has a constant taper, it is simple math/geometry.
now i don't know if ibanez has the same width at the heel as fender but i'll assume it's close so you'll want a similar nut width as an ibanez, now ibanez has more than one nut width so what model ibanez are you talking about? ibanez is measured in metric so you'll need to just get the closest one. i think the narrower ibanez nuts are closer to 1-11/16 and the wider are just under 1-3/4.