.I would not say your grey is not smart, After all, when Tezy poops who clesns it up, Not tezy.
My grey Corky will poop on her T-Stand when she is out of her cage.
This may help.
A grey will poop about every 20 to 30 minutes and before they poop they give a sign of the comming atraction like a tail wiggle.
Time your greys poop cycle as differant greys and there diet may be defferent from one anouther.
Once you know your greys poop cycle you will time from one cycle to about the next one and watch for Tezts sign or just put her on a T-Stand or where you want her to go and say go potty or bombs away or something like that and when Tezy poops tell her GOOD TEZY !!!! and than wait for the next cycle and do it over again.
It took Corky about 4 or 5 cycles and she had it down. Make sure that you praise her each time she poops on the perch or where ever you want her to go.
Praise Tezy every time she goes where you want her to. Just remember you have to take her to her poop place in the cycle and if you miss its your fault and not hers.
In time she will go to the spot on her own just to make you happy and some times there will be an accident. Thats life.
Always watch for the poop dance and the tail wiggle
P.S. Never force a poop by doing it to close together, Its not good for them.