It's not about the fan survey much. The incomes have been very steady all the time, no matter how well I played. Mostly 32k to 40k, if I remember well.
Well, if new teams are given a special consideration regarding the fan survey, then perhaps yours just ran out. I can say from tracking merchandise since Season 18, that promotion absolutely increases merch, and absent a promotion bonus, the fan survey definitely affects merch.
Seems that the income is calculated by the salary structure, not the salary total much.
With my 40k homegrown roster I earned 40k. Now, I still have my home players, but my foreign player takes about 70% of the new total paycheck(130k)
Yes, I definitely agree that total salary doesn't affect jack. I have my team's highest salary now, and weakest overall merch (since I've been in D3).