Boar breeding problems, Help Please

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I sold one of my boars to a friend with 2 gilts and 3 sows. He is a 1 1/2 year old exotic, crossed to a registered Hampshire. He is taller framed than what we have seen the last few years and has plenty of length. He has been successful in settling a sow and a gilt both will be farrowing in August. His attempts to breed the others has been unsuccessful. The breeder that has him explained that he does not appear to be extending himself. Last week she was able to watch him attempt to breed an older sow. The sow would back up to him and she would see him ejaculate without extending out of the sheath.
The boar is allowed to roam freely with the girls and he stays busy enough with the three open girls but not too busy as they are not cycling at the same time. I'm not sure why he was able to settle two of her pigs with no problem extending and now he is.
Any suggestions
Thanks
What was I thinking