The real constraint
Your CAC is probably wrong, and it is wrong in a flattering direction
Most SaaS acquisition reporting credits the last click before signup.
That systematically over-credits branded search and retargeting —
which capture demand that already existed — and under-credits
whatever actually created it. Budget then flows toward the channels
that look efficient precisely because they are harvesting.
The second problem is that signup is not the outcome. A trial that
never activates is a cost, not a win. Optimising the ad account
toward signups will reliably buy you more of the cheapest, least
serious ones.
We rebuild the measurement around activation and paid conversion
first, then argue about channel mix. Usually the argument settles
itself once the numbers are honest.