An example of what I see when looking at a return flight BHX-IST-BOS


Now I know BHX-BOS is more than 1635 miles!
So I looked up the table to check the fare class was not the culprit

According to this table both Q and H fares should be getting 3184 miles credited (6368 roundtrip). But on the booking page I see 1635. Is this some sort of glitch in their software. Sometimes I've seen an outbound leg with say 8000 miles and an inbound with around 1500 and they are the same fare class. Is it some kind of lottery. Does the table have precedence over whats stated on the booking page or can the table be relied on?

I also noticed... "Miles amounts shown in this table are for informational purposes only and subject to change"