The Dway fit note is a reference-level instruction
Dior's white calfskin and embroidered-cotton Dway slide page states that the style fits large and recommends a half size smaller than normal. That is unusually direct and should be carried into the search, but it does not convert every Dior slide automatically. D-Lane and 30 Montaigne slides are separate references with their own constructions. Use the note for the Dway after confirming that the listing is actually that model. Ask for the reference code visible on the product or box, because the word slide can describe a flat, a heeled version or an openwork upper with a completely different last.
Insole and outsole are different lengths
The Dway page describes a padded cow leather and TPU insole over a calfskin sole. That layered construction is why an outer sole measurement includes material beyond the footbed. Ask the seller to photograph a tape from the heel cup to the front edge of the insole, following the footbed rather than the outer edge. If the tape runs across the top surface of an embroidered slide, it should not be pressed into the upper. Repeat the figure on both shoes when possible. A half-centimetre difference can decide whether the toes sit behind the front edge.
The upper changes how the marked size feels
Calfskin and cotton embroidery have less give than a simple textile band, while an openwork Microcannage upper removes material and changes where pressure lands. The slide has no laces, buckle or adjustable strap in the flat Dway construction, so length and footbed width are the only controls. A high instep can make the upper sit tighter without making the footbed shorter. Compare the width across the ball of the foot, not only the length. If the pair fits at the heel but presses over the toes, do not assume a larger size solves every point; a different upper may be the better answer.
Use the EU label with a centimetre record
Dior women's shoes are labelled in IT/EU sizes, and published reproductions of the Dior foot-length chart assign slightly different centimetres to the same label. Record the EU figure and the longer foot in centimetres together. For the Dway, apply the published half-size-down instruction after identifying your normal size on the exact ladder. For another slide, do not carry that adjustment over automatically. The reference and its printed fit sentence provide the safest route from the label to the pair.
A three-photo slide check
Ask for a top view with both slides closed beside each other, a side profile that shows the sole and any heel, and a close view of the inner stamp and footbed. The top view reveals whether the pair is symmetrical and how much toe room remains; the profile shows the sole thickness; the stamp identifies size and sometimes the material. Add a tape measurement of the insole. Those four pieces of evidence answer fit without requiring another person to judge the colour or lighting of a single angled photograph.