Is it possible to go above 350F with Excel 20 as kettle gril

After successful smoking a few spareribs with my new ProQ Excell 20 using the waterpan and 1 stacker, today I tried to bake a pizza with it. I only used the base and the lid, thus as a kettle. I put a full chimney with lit briquettes in it, in a circle, and put my Weber pizza stone on the grate. Even after 45 minutes I still was at 350F and could not get higher, although all the vents were open.
So I wonder, should it be possible to achieve higher temperatures and how should I do that ?

Took mine up to 550 Deg F using the same configeration last night, using just normal briquettes, the basket was only 1/2 full.

So it must be possible, but what could I have done wrong then ?
Do you have any tips or advice ?

I quite often do teryaki pork belly high and direct. That's two stackers no water pan, grill on top one with lid on. I get 450 doing at the grill burning 2/3 basket of lump. So I don't know how you couldn't get above 350. I run with vents fully open to get the fire raging. You weren't doing minion were you?

No, I did not use the minion method and I only used the base unit and the lid.
I lit a full (Weber) chimney starter with a mix of Weber briquettes and lump charcoal and arranged it in a circle in the ring. I did that - the circle - because I read that otherwise there is a chance that the pizza get burnt.

Ton, I think it may be something to do with the Weber Briquettes, I get a lot of complaints about people not being able to get much heat out of them.

Ian, meanwhile I asked the members on our dutch bbq forum for their experiences with the Weber briquettes. Got some replies saying that with Weber they often get higher temperatures than with other brands.
I will soon give it another try.

Tonight I did some steaks, using the Excel 20 as kettle again and with a full chimney with Weber briquettes now I could get above 500F.
At second thought, I think I had some leftover, partially burnt, briquettes in the chimney as well, so maybe that may have contributed.

Glad you managed to get it up to the desired temp Ton.

Also glad you managed to get your temperature, also I second Ian on the Weber briquette comment. I find them a sod to light and then they don't burn that hot. Also they leave a horrible yellow ash behind which I really don't like the look of, don't know what binder they use but it doesn't look dood to me.

Last weekend I bought 7 (7kg) bags of these Webers, because the store that I visited happened to have a special weekend with 30% discount on their whole assortment, so it would be a waste not to use them.
But maybe it is not that bad, given my last experience and the opinions on the dutch forum.