Confusion related to leasing and buying tax timing rules

According to what you said today about the lease and buy rule in this thread (https://opentuition.com/topic/npv-investment-appraisal-tax-timings) I needed to know this thing from a different perspective.

If tax is in ARREARS (ie tax paid one year later):

1) If First CashFlow is on First day of accounting period then First Tax effect is at Time 2;

Example:
Lease Payments were at the start of the period at Time 0 (1.1.2017) so tax is calculated at the end of the period at Time 1 (31.12.2017) but since tax is in arrears so it is one-year delay at Time 2 (31.12.2018)

Similarly, if the Machine was bought at the start of the accounting period at Time 0 (1.1.2017) so the same way is followed and the tax is paid at Time 2 (31.12.2018)

2) If First CashFlow is on Last day of accounting period then First Tax effect is at Time 1;

Example:
Machine was bought on last day of the period so tax is calculated immediately at the end of the year at Time 0 (31.12.2016) but since tax is in arrears so it is one-year delay at Time 1 (31.12.2017)

Similarly, if the Lease Payments were on the last day of accounting period at Time (31.12.2016) so the same way is followed and the tax is paid at Time 1 (31.12.2017)

3) Both of the rules (1 and 2) above are not only for Lease Payments AND Capital Allowances on the machine but rather apply to any cashflows?

4) Why do we assume that the year started for Leasing is 1 Jan 2017 but the year for Buying started from 1 Jan 2016?

Please correct me and have a look at my examples whether they are also correct or not.