I find it strange as well. Blocks $1 and $14 were purchased by the same app developer as they wanted presumably the top left and top right position when I firs

I find it strange as well. Blocks $1 and $14 were purchased by the same app developer as they wanted presumably the top left and top right position when I first launched the site. Ever since then it's been going up incrementally. I think what happened was that the app developer who purchased block 15 was indicating to me that he might purchase block 16 AND block 29 and 30 so that the same icon would stand out (4 icons grouped together). This never eventuated, so it appears to the eye if scanned quickly that block 16 was the next one in line which was subsequently purchased by another app developer. It's that or 13 is an unlucky number for some. Especially if purchased on a Friday. :-)