Trying to predict air fares is a black art akin to chicken bones and roulette!
For example Luton-Dalaman in June and September has a low of about £64 outbound and about £250 inbound.
And that's just the ones I looked at, before the extras!
I think the main factor is "How low (price-wise, that is) do we have to go to shift these seats?".
On the other hand Monarch are cheap when they go on sale, and tend to go up until the New Year.
But not always!
My head hurts!!!