Minimum Spot Bid Price and "hardware costs"

Question

While trying to update the max price per hour for a spot VM in the portal, I am unable to set it lower than 40% of the pay as you go rate. This is despite all available pricing information sources stating that the current spot price is much lower (~20% of PAYG).

When trying to set it to a lower value, the portal displays the following error message:
"Enter a price greater than or equal to the hardware costs (US$0.23160)"

The spot pricing for the NCas_T4_v3 according to this page is $0.1227/hour at the time of writing this question.
A query to the "Retail Prices REST API"(available here) specifies the current spot price as $0.122667/hour.

The pricing history for the VM type also shows a drop in price:

Running the VM at a max_price of -1 results in a charge of ~$0.24/hour. I managed to set a lower bid using the Azure CLI interfaceas follows:

az vm update --resource-group MyResGroup --name MyVmName --max-price 0.13

The VM did run for about 20 min after which it was evicted. That seems like expected behavior.

1. What is this minimum "hardware cost" and how is it related to the spot prices mentioned elsewhere?
2. Is it possible to get fine grained spot pricing history? Something like min and max within a particular time window.
3. Is the inability to set max price in the portal a bug? Considering the CLI accepted the max-price without issues.