Ok from our experience. Firstly different companies and different countries have very different idea of what they want. The German companies seem to have taller girls and thus need the tall lads. Martin noticed whilst auditioning that places such as Portugal the dancers seemed smaller.
However most companies have a minimum height for audition. For Munich (where Martin is) it was about 5ft 10/11 for boys. I think other companies were around 5ft 8".
Girls are taller in companies than they were. I know some of the little girls did struggle to get contracts irrespective of their talent.
Re physique. My son was and is very slim and this did impact. There were concerns as to his strength. However now, aged 22, though slim he is muscular and does not look out of place. He took time to develop and did grow a couple of inches between year 10 and 13.
Sorry this probably doesn't help much. Finally though I think, in Martin's year, one of the smallest lads was the first to get a contract.
Good luck.