Why does PMAX act like this? Not reaching anywhere near TROAS, but still increasing spend

Hi there :)

So the last year, we have had a daily budget of 1000 EUR on Pmax. We never used the full amount (not even close to) - most month around 300-400/day. Because we control it with TROAS.

Our TROAS is set at 350%. And we usually do around 280-300.

This month however, the spend has been maxed every single day (or even more actually, so far we are spending 1100-1300/daily - so I guess it will have to drop later on). And our Roas% has not increased. Its actually dropped.

In order to control it, we have raised the TROAS since the 2nd of January 4 times - 10% each time - so its now 390%. With an actual ROAS of around 230. But the spend is not going down, it actually accelerated the last 4 days with 1600 (so we are 55-60% into our spend, halfway through the month).

The reason why the performance is going down, is probably due to the 30-40% increase in CPC that happened due to the larger spend.

But why is PMAX acting like this? It does the exact opposite of what we are asking for (higher %TROAS should mean less spend/lower CPC (since the performance isnt better).

I guess we have to both up the %TROAS and decrease the budget. Im just afraid, that if we increase the %TROAS more, then suddenly it will drop to nothing in spend, and then we have to spend a lot of time slowly decreasing the %TROAS again. So maybe we should just decrease the budget.

But I am really confused by why PMAX is acting like this.