Two teams can arrive at a fixture with the same recent record and be entirely different propositions. Splitting form by the quality of the opposition faced is the fastest way to see it.
A form table hides the opponent
The standard last-six display shows results and nothing about who produced them, so a run against the bottom of the table looks identical to one against the top.
Because fixture lists are unbalanced over short periods, this difference is present in almost every form guide published.
It is also the largest single distortion in the whole measure, and correcting it requires only a glance at the league positions of the opponents.
The two profiles behave differently
A team that beats weak sides comfortably and loses to strong ones is usually built around control, and it struggles when it cannot dictate the pattern.
A team that takes points from strong sides and drops them against weak ones is usually built to defend and counter, which needs an opponent willing to attack.
Neither profile is better. They are simply suited to different fixtures, and the next opponent determines which one is relevant.
Style matchups drive much of it
A side that defends deep and breaks quickly is a poor fit against another deep block, because there is no space behind to run into.
The same side facing a high line has an obvious route to chances, which is why it can look transformed from one week to the next.
Reading this requires knowing how the upcoming opponent plays rather than only where it sits in the table.
Promoted and relegation-threatened sides complicate it
Teams near the bottom often change approach depending on the fixture, defending deep against strong opponents and pressing against peers.
Their form against the top half therefore reflects a different version of the team from the one that plays their direct rivals.
Splitting their record is especially informative, since the two halves can point in opposite directions.
How to build the split quickly
Take the last ten matches, mark each opponent as top half or bottom half at the time of the fixture, and total the two groups separately.
Where the two totals diverge sharply, the aggregate form figure is meaningless and should be discarded entirely.
Where they agree, the form guide is telling the truth, and that agreement is itself the most useful thing the exercise produces.