What i assume is the reasoning about smaller closeups is that it is a good compromise between showing more steps of the "act" and not drawing whole new pics for a single scene. See, the "animation" you watch during most CGs now is made through doing a few alts of one pic, you change some things, set them in a loop, and it looks animated (you can see some very old scenes did not use this loop trick, but had alts nonetheless); the smaller closeups provide a different point of view and can show there was some sort of progression during sex, while drawing a full picture (plus bigger alts coming with it) would be way more work and even be inconsistent with former CGs.
Still, i did find the closeup covered a bit too much of the main pic behind for the katos, i kinda wanted to tell Caro about it.