Leakage inductance of "short spindle" flyback transformers is high?

TI has a document on Designing Planar Magnetics which you might find informative:
https://www.ti.com/download/trng/docs/seminar/Topic4LD.pdf

Thanks . Great document, but on the first page they confess that planar transformers tend to have greater winding loss than wire wounds, when used with gapped cores...

However, in inductors and flyback
transformers using gapped centerlegs, the
winding configuration often results in greater
AC winding loss.

Click to expand...

on page 4-3 the document also confesses that the lowest leakage can be obtained with wire wound transformers..

Bifilar windings approach the ideal, but this
is usually not possible in a planar transformer,
especially when high voltage isolation is required.

Click to expand...