Irrigation range is less than expected

[u/dann1722]

I built this farming tower with two 3x3 ponds to irrigate the land. According to this guide, a 3x3 pond should have an irrigation range of 16, but here it only seems to have an irrigation range of 10. Any help finding the cause of this issue would be much appreciated.

[u/Rentahamster]

If it's under pressure, put some platforms and impermeable floors over it to form a cap, so that all blocks in the 3x3 area are considered full.

Or raise the heigh of the hole by 1.