Using Hardhat forking blocknumber and delays

Question

I've just tried to make a transaction in the past in block number 15981826 using Hardhat forking:

  networks: {
    hardhat: {
      forking: {
        url: "https://mainnet.infura.io/v3/",
        blockNumber: 15981826,
        allowUnlimitedContractSize: true,
        gas: "auto",
        gasLimit: 21000,
      },

In my main file I'm using this provider

const provider = new ethers.providers.JsonRpcProvider("https://mainnet.infura.io/v3/");

const tokenBase = new ethers.Contract(importToken1, abi, provider);
const [deployer]= await ethers.getSigners()

//Standart contract deploying with helpers

 const SwapExamples = await ethers.getContractFactory("FlashLoanRecipient")
    swapExamples = await SwapExamples.deploy()
    await swapExamples.deployed()

And after deployment I'm checking blocknumber:

  block = await ethers.provider.getBlockNumber()
    console.log(block) //result : 15981828 (+2 blocks)
    block = await provider.getBlockNumber()
    console.log(block) //result : 15982414 (current block)

I'm laucnhing my file with command :

node test/swap

, but even with

npx hardhat run test/swap.js

result is the same.

Seems like I don't fully understand the difference between data from ethers.provider and ethers.providers.JsonRpcProvider.

ethers.providers.JsonRpcProvider("https://mainnet.infura.io/v3/") - is a real time info from blockchain and ethers.provider.someMethod - is an information from Hardhat?

And my last "test" was without any blocknumber input:

 block = await ethers.provider.getBlockNumber()
    console.log(block) //result : 15982499(-4 blocks from current)
    block = await provider.getBlockNumber()
    console.log(block) //result : 15982503(current block)

So I have 4 questions:

1. Why do I always have +2 blocks difference from what I have in config?
2. Why there is a delay in 4 blocks between provider and ethers.provider?
3. When I'm using forking mainnet in Hardhat without any blocknumber parameter, is it a real time situation in the mainnet or it's also a couple of blocks delay?
4. How can I get to exact block that I need?

Thanks.