I believe Reagan chose Bush as his VP to unite the party. Bush’s decisive win in the Michigan primary in May, 1980, demonstrating that he still had voter appeal despite a string of primary defeats, may have convinced Reagan to do so.
Poppy politically & social issues was much closer to Ford than Reagan so yeah that makes sense. Up till then VP didn't really carry that much say or influence in polices except in event of a tie vote in the senate. I think though due to early Alzheimers Bush likely had more influence in Reagan's second term than he otherwise would have had except on possibly Intel issues which is the only other reason I could see other than unity for Reagan picking him.