The Dway fit note is a reference-level instruction
Dior's white calfskin and embroidered-cotton Dway slide KCQ986CEY_S03W states on its own product page that the style fits large and recommends taking half a size, 0.5, smaller than normal. That is unusually direct guidance for a slide and worth carrying into a search, but it applies to that reference rather than to Dior slides as a class. The Dway heeled slide KCQ915ERC_S56B, the D-Lane with its openwork Microcannage calfskin KCO157MLC_S900 and the black calfskin 30 Montaigne KCQ266VEA_S900 are separate last shapes with their own uppers, so a half-size adjustment tested on the flat Dway does not transfer to a heeled version carrying the same name. Those four references differ in upper, sole and heel, which is why the model name alone cannot settle a size question. Ask for the code printed on the slide or its box before applying any fit note.
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 give less than a plain textile band, and an openwork Microcannage upper removes material altogether, so two slides marked the same size press in different places. The flat Dway has no lace, buckle or adjustable strap: the upper is one continuous band over the instep and the footbed is the only other contact point. That removes every tuning option except length and width across the ball of the foot, which is why the insole figure deserves more weight here than on an adjustable sandal. A high instep makes the band sit tighter without the footbed being short, so a pair that presses over the toes may still be the correct length. Dior labels women's footwear in IT/EU sizes from 34 to 42 with half steps between, so record the EU number and the longer foot in centimetres together.
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 three photographs and one tape measurement. A top view with both slides side by side shows whether the pair is symmetrical and how much toe room remains in front of the strap; a side profile shows the sole thickness and whether the reference is flat or heeled, which is the visible difference between the Dway and the Dway heeled slide; a close view of the footbed stamp identifies the size, the reference code and sometimes the material. Then ask for the insole measured from heel cup to front edge, following the footbed rather than the outer sole, because the padded cow leather and TPU insole sits inside a calfskin sole and the outside always reads longer. With those four pieces of evidence fit can be judged from numbers instead of from one angled photograph and a colour description.