Seats and placements in an 8: why do they work?

Typically the middle four seats are the “power house”. These are the people who might not have the best form, but are definitely the strongest.

The outer 2 seats on either side (1,2,7,8) are taken by those who have better form. This doesn’t mean that they are weak however.

Strong rowers tend to be bigger, so fit better in the 4 inner seats. Granted you are a strong rower with good form, you may be placed in the middle seats purely because of good fit.