You have discovered something about fitting that the "TrackMan" people discovered exists even on the PGA Tour among pros who you would think are as consistent as can be in the manner in which they deliver the clubhead to the ball at impact.
The idea of irons being made so the change of loft from club to club is the same number of degrees only delivers the same distance increment between the clubs if the golfer delivers the clubhead to the ball with each club in exactly the same manner. Clubs do differ in length and in total weight and in lie. These things along with each golfer's own way they set up to the ball and swing each club can contribute to the golfer delivering the clubhead slightly different to the ball with the different clubs in the set.
If these things result in the clubhead having a little different dynamic loft at impact, the distance difference between clubs that are separated by the same number of degrees of loft will then be different.
TrackMan showed that in many cases with the tour pros because of these little differences, they had to bend the loft into quite a different spacing of degrees to end up delivering the same exact number of yards between each club in the set.
With average golfers who do not have that high of a level of consistency for ball position, for angle of attack into the ball, for swing path and swing plane with the different clubs, it very well may be that such odd types of loft adjustment may have to be done to end up giving the golfer the same number of yards between clubs.
However, the FIRST thing to do in these situations is to do a very accurate loft measurement on all the irons. As we have mentioned several times, the very best foundries in the world cannot and do not manufacture clubheads with better than a +/-1* tolerance for loft (and lie and face angle).
This is not to say that a very high number of heads actually are off by +1 or-1 for the loft - they aren't because what makes a foundry really good in this business is the fact that the number that are off by +1 or -1 is a pretty small number. But it still can happen. So start first if you can with a very accurate loft measurement to see where the adjacent irons are at, and then from that, work on making the fine tuned loft adjustments that result in a more even spacing for distance between the clubs.
Last point, do NOT rely on the loft measurement part of a loft and lie machine to do the loft measurements. This part of a L/L machine is not as reliable for accurate loft measurement as a specs measurement machine/gauge. For accuracy all spec measurements have to be done on a separate specs measurement machine or gauge.