Sounds like you are compacting the rootball with your watering technique, and the roots are likely air-pruning themselves around the perimiter of the rootball as a result. Moisture and nutrient uptake are likely at a minimum, plus you damage roots.

Don't do that any more.

Late flower soil decline is common. Seems to get a crust, and moisture retention fades.
If having problems with soil not absorbing moisture when watered, and everything flows straigh through...try adding a teaspoon of non-antibacterial dishsoap per gallon of water, for a couple of consecutive waterings. The non-antibacterial dishsoap (don't kill your soil biology) acts as a surfactant, and the soap bubbles actually hold some of the moisture till the medium decides to absorb it. Should carry you through till harvest. :thumbsup: