The thing to rememmer about session tunes is that they were originally for dancing and that the dances can go on longer that an individual tune.

But as long musicians keep the tunes in the set to all reels or or jigs - dancing can still take place and the musicians can do as they wish to ensure they don't get too bored. There are really no rules as far as the keys (modes) of the tunes in a set - as there is no need for this.

Although anyone attempting to dance a set or reels at the speed that some sessions now play them - would have to be very fit - or probably die in the attempt............