Combine A5 into A4 pdf without scaling

For our ceilidh band we keep the sheet music for our tunes as a folder of landscape A5 pdf documents. I combine these into a portrait A4 tunebook with 2 tunes on each page. To do that I use Preview and the print option Layout > Pages per Sheet set to 2. So far so good.

But the music always ends up a little scaled down. Smaller than it would be if you just put two of the original A5 pages one about the other.

Is there a simple way to avoid that scaling? I've tried adjusting the percentage in the Scale setting (153% seems to produce a reasonable result). But it feels like I'm missing the 'just print the pages at their original size' setting.