it depends on a lot of variables. How deep did you amend? how much growth was there? are the earthworms forced to go up and down by winter freezes? Most of the drainage comes from root or EW channels, the deeper the better. at any rate, I think amending is inferior to cover cropping when it comes to drainage.

Also depends on the native soil conditions. In clay, the part amended may become a bathtub and actually be more soggy since the surrounding clay will give up its water to the more permeable soil. OTOH if the amending resulting in fluffing, the bed will be slightly raised and will most likely drain better. In either case I don't think the unamended part would benefit much.

Interesting read so far. In the so called scenario of half/half, it more or less applies to what I'm understanding on soil where I don't really touch (like the lawn) and just the adjacent beds which are ~fluff~. I'm never done planting so the occasional times I'm digging deep, while I am seeing the improved soil, if I dig deep enough, I'm still seeing water rentative clay.

On my gardens there is about a 1% slope on 2 of them and the third garden is a little higher up. I have made sure that there is physical drainage to lower areas at the lower ends.

Then I have amended deeply with sand, peatmoss, leaf compost, leaf mulch, and horse manure.

I started with decent silt loam soil and silty clay loam in a couple lower corners.

The result...dream soil that is a bit higher and absorbs water like a sponge and is very very friable.

Below is a link to soil types. Some are sandy. Some are silty. Some are more clayey. None likely are just clay. .. One soil type

Another Soil Type

another soil type yet