Quarter-page adverts serve as a quick reminder of previous, larger adverts. Or can be used if advertising space is at a premium in a popular magazine. The advert above is from Striker, and came after the first colour full-pager and two half-page adverts over several issues. The four vehicles have been taken over from (the paste-up artwork for) the full-page adverts.
The advert below is from a Tiger and Jag comic magazine published a week later, and is as far as I know the only Spacex advert in that magazine (I would love to be told otherwise, though!). It shares a page with a space adventure story, which may account for its presence.
Advert at top from
< 11 July 1970
Advert above from
18 July 1970 >